Summary of Cognitive Neuroscience: The Biology of the Mind by Gazzaniga a.o. - 5th edition

The goal of cognitive neuroscientists is to figure out what the 89 billion neurons of the human brain do and how their collective action enables us to function. 

What are the cells of the nervous system?

The nervous system is composed of two main classes of cells: neurons and glial cells. The neurons are the basic signaling units that transmit information throughout the nervous system. They vary in form, interconnectivity and location. Glial cells serve various functions in the nervous system, providing structural support and electrical insulation to neurons and modulating neuronal activity. 

Glial Cells

There are roughly as many glial cells as there are neurons in the human brain, the central nervous system has three types of glial cells: astrocytes, microglial cells, and oligodendrocytes. 

Astrocytes: are large glial cells with round or radially symmetrical forms, they surround neurons and are in close contact with the brain's vasculature. They make contact with blood vessels, which permits the astrocyte to transport ions across the vascular wall.

The astrocytes create the Blood Brain Barrier. This lies between the tissues of the central nervous system and the blood. The BBB makes sure certain microscopic objects, such as bacteria, can't diffuse into the blood vessels. The astrocytes also have an active role in brain function. They may either directly or indirectly regulate the reuptake of neurotransmitters. 

The glial cells also form the substance myelin in the nervous system. In the central nervous system the oligondendrocytes form the myelin, in the peripheral nervous system the Schwann Cells perform this task. Myelin is a good electrical insulator, preventing loss of electical current across the cell membrane. It increases the speed and distance that information can travel along a neuron. 

The microglial cells are very small and irregular shaped. They devour and remove damaged cells. 

The Neurons

A neuron consists out of the standard components found in almost all cells. They have a cell membrane, sometimes called a soma that encases the cell body. It contains the nucleus, endoplasmic reticulum, cytoskeleton, mitochondria, Golgi apparatus and other organelles. The neuron itself sits in a bath of salty extracellular fluid, which is made up out of a mixture of ions (positive or negative electrical charge; potassium, sodium, chloride and calcium). 

Neurons possess two unique cellular components: the dendrites and the axon. The dendrites are branching extensions of the neuron that receive inputs from other neurons, they can have varied and complex forms depending on the task and location of the neuron. Most dendrites also have specialized processes called spines, little knobs attached to the surface of the dendrites. The axon is a dingle process that extends from the cell body. Electrical signals travel along the length of the axon to its end, axon terminals, where the neuron transmits the signal to other neurons or other targets. The transmission of the signal occurs in the synaps. Some axons can branch to form a axon collaterals that can transmit signals to more than one cell. 

Neurons receive, evaluate, and transmit information, this is called neuronal signaling. Information is received by the neuron at its input synapses, passes through the cell body, via the axon, to the output synapses on the axon terminals. Within the neuron information moves from input synapses to output synapses through changes in the electrical state of the neuron caused by the flow of electrical currents within the neuron and across its membrane. Most neurons are both presynaptic - when their axon's output synapses make connections to other neurons or targets - or postsynaptic - when other neurons make a connection at the input synapses onto their dendrites or elsewhere on the receiving neuron. 

How does the neuron generate signals, and what are these signals? To answer these questions you first have to understand several things about a neuron:

1. Energy is needed to generate the signals

2. This energy is in the form of an electrical potential across the neuronal membrane, this is defined as the difference between the voltage inside the neuron versus outside the neuron

3. These two voltages depend on the concentrations of potassium, sodium and chloride ions, as well as on the charged protein molecules both inside and outside the cell

4. When a neuron is in its resting state and not actively signaling, the inside of a neuron is more negatively charged than the outside, this difference is typically -70 mV, this is known as the resting membrane potential

Also, the neuron membrane is peppered with transmembrane proteins, these are of two main types: ion channels and ion pumps. Ion channels are proteins with a pore through the center and they allow certain ions to flow down their electrochemical and concentration gradient. Ion pumps use energy to actively transport ions across the membrane against the concentration gradient. 

The extent to which a particular ion can cross the membrane is referred to as its permeability. This characteristic gives the neuronal membrane the attribute of selective permeability. The neuronal membrane is more permeable to K⁺ than Na⁺. Unlike most cells in the body, neurons are excitable, meaning that their membrane permeability can change, such proteins are called gated ion channels. 

Regarding the ion pumps; Under normal conditions, the NA⁺ and the Cl^- concentrations are greater outside the cell, and K⁺ concentrations are greater inside the cell. Why don't the K⁺ just flow out of the cell until the concentrations are equal inside and outside the cell? Neurons use active transport proteins known as ion pumps. They pump Na⁺ out of the cell and K⁺ into the cell, but this costs energy. Each pump is an enzyme that hydrolyzes ATP to get that energy. The inside and outside voltages are different because the membrane is more permeable to K⁺ than to Na⁺. The force of the K⁺ concentration gradient pushing the ions out of the cell, leaving the inside of the cell slightly more negative than the outside. This difference creates another force called electrical gradient. Eventually, the force of the concentration gradient pushing K⁺ out of the cell through the channels is equal to the force of the electrical gradient driving the K⁺ in. When this happens there is said to be reached an electrochemical equilibrium. 

The action potential

Neurons have evolved a clever mechanism to regenerate and pass along the signal received at synapses on the dendrite: the action potential. An action potential is rapid depolarization and repolarization of a small region of the membrane. Action potentials enable signals to travel for meters with no loss in signal strength, because they continually regenerate the signal at each patch of membrane on the axon. The action potential can regenerate itself by voltage-gated ion channels. The ion channels are also found along the axon. In myelinated axons, voltage-gated ion channels along the axon's length are restricted to the nodes of Ranvier

1. The depolarized membrane (-55mV) is the potential value for the threshold for initiating an action potential. When the threshold is reached the voltage-gated Na⁺ channels open and the ions flow rapidly into the neuron. This influx of positive ions further depolarizes the neuron, continuing the cycle by causing even more Na⁺ channels te open. 

2. This is called the Hodgkin-Huxley cycle. This lasts about 1 ms and generates the large depolarization that is the first portion of the action potential. Then the K⁺ channels open, allowing the ion to flow out of the neuron to down its concentration gradient. This outward flow of positive ions shifts the membrane back toward its resting potential. 

3. The opening of the K⁺ channels outlasts the closing of the Na⁺ channels, causing a second repolarizing phase of the action potential. This drives the membrane toward the equilibrium potential of K^+.. The membrane is temporarily hyperpolarized (-80 mV). 

4. Hyperpolarisation causes the K⁺ channels to close, in reponse to which the membrane potential gradually returns to its resting state. (-70 mV).

5. During this transient hyperpolarisation state, the voltage-gated Na⁺ channels are unable to open, so not other action potential can be generated. This is called the absolute refractory period. This last only a couple of milliseconds and has two consequences:

   1. The neuron's speed for generating action potentials is limited to about 200 action potentials per second. 

   2. The passive current that flows from the action potential cannot reopen the ion-gated channels that generate it. The result is that the action potential moves down the axon in one direction only, from the axon hillock to the axon terminal.

What holds the synaptic transmission?

Most neurons send a signal to the cells across the synapse by releasing chemical neurotransmitters into the synaptic cleft, gap between neurons at the synapse. 

1. The action potential at the axon terminal leads to depolarization of the terminal membrane and opening of the voltage-gated ion Ca²⁺ channels. 

2. This opening triggers small vesicles containing neurotransmitter to fuse with the membrane at the synapse and release transmitter into the synaptic cleft.

There are two types of postsynaptic receptors: ligand-gated ion channels - where neurotransmitter binding directly gates (opens) the ion channel, and the G protein-coupled receptors where biochemical signals indirectly cause the gating of the ion channels, this works via a second messenger. 

The neurotransmitter

What makes a molecule a neurotransmitter?

• It is synthesized by and localized within the presynaptic neuron, and stored in the presynaptic terminal before release. 

• It is released by the presynaptic neuron when action potentials depolarize the terminal

• The postsynaptic neuron contains receptors specific for it

• When artificially applied to a postsynaptic cell, it elicits the same response that stimulating the presynaptic neuron would.

Some neurotransmitters are amino acids: aspartate, GABA, glutamate, and glycerine. Other neurotransmitters are dopamine, norepinephrine, and epinephrine, serotonin and histamine. Another large group of neurotransmitters consists of slightly larger molecules and are called the neuropeptides; tachykinins, neurohypophyseal hormones, hypothalamic releasing hormones, opioid peptides and other neuropeptides. A particular neurotransmitter may have more than one type of postsynaptic receptor to which it binds, mediating different responses. The neurotransmitters that usually have an excitatory effect include ACh, catecholamines, glutamate, histamine, serotonin, and some other neuropeptides. The neurotransmitters that usually have inhibitory effect include GABA, glycine and some of the neuropeptides. 

The two primary players in balancing act between excitation and inhibition are glutamate and GABA. Glutamate is released by the pyramidal cells of the cortex, therefor it is the most prevalent neurotransmitter and is found in most of the fast excitatory synapses in the brain and spinal cord. GABA is synthesized from glutamate. It is found in most of the fast inhibitory synapses across the brain. 

Acetylcholine is present in the synapses between neurons and between neurons and muscles, where it has an excitatory effect and activates muscles. 

The primary sites of dopamine production are the adrenal glands and a few small areas of the brain. This include the striatum, substantia nigra and hypothalamus. There are several dopaminergic pathways, each sprouting from one of the small brain areas and is involved in several functions including cognitive and motor control, motivation, arousal, reinforcement, reward etc. 

Serotonin in the brain is released largely by the neurons of the raphe nuclei, in the brainstem. The serotonergic pathways are involved in the regulation of mood, temperature, appetite, behavior, muscle contraction, sleep and the cardiovascular and endocrine systems. 

Norepinephrine or noradrenaline is the sympathic nervous system's go-to neurotransmitter. It is produced by neurons with cell bodies in the locus coerculeus - area in the brain involved in physiological reactions to stress and located in the brainstem, more precisely the pons. Outside the brain NE is released by the adrenal glands. There are two types of receptors for NE: alpha-1 and alpha-2, and beta. The alpha-2 receptors tend to have excitatory effects, the alpha-1 and beta receptors tend to have inhibitory effects. 

Some neurons communicate via electrical synapses, which are very different from chemical synapses because there is no synaptic cleft that separates the neurons. The neuronal membranes touch at specializations called gap junctions, and the cytoplasms of the two neurons are essentially continuous. As a result, the two neurons are isopotential, meaning that electrical changes in one are reflected instantaneously in the other. 

What is the overview of the nervous system structure?

Neural communication depends on patterns of connectivity in the nervous system, the neural 'highways' along which information travels from one place to another. But identifying those patterns is tricky because neurons are extensively connected in both serial and parallel circuits. Localized interconnected neurons form a microcircuit. They process specific kinds of information and can accomplish sophisticated tasks such as processing sensory information, generating movements and mediating learning and memory. 

There are long-lasting connections between various brain regions, those are called neural networks, which are macrocircuits that are made up of multiple embedded microcircuits. 

The two main divisions of the nervous system are: the central nervous system (CNS) consisting of the brain and spinal cord and the peripheral nervous system (PNS) consisting of nerves and ganglia outside the CNS. 

The autonomic nervous system

The autonomic nervous system is involved in controlling the involuntary action of smooth muscles, the heart and various glands. It has two subdivisions: sympathetic and parasymphathetic branches. In general, the sympathetic system uses the neurotransmitter norepinephrine, and the parasympathetic system uses the neurotransmitters acetylcholine. The two systems frequently operate antagonistically. 

The central nervous system

The CNS is made up of the brain and spinal cord, and each is covered with three protective membranes, the meninges. Between two membranes is the subarachnoid space filled with cerebrospinal fluid (CSF). Within the brain there are four large interconnected cavities called ventricles. The largest are the two lateral ventricels in the cerebrum, which are connected to the more caudal third ventricle in the brain's midline and the fourth ventricle in the brainstem below the cerebellum. The CNS neurons are bunched together in various ways, two of the most common organizational clusters are the nucleus and the layer. Nuclei are located throughout both the brain and the spinal cord. The cerebral cortex of the brain, on the other hand, has billions of neurons. The cerebellum is the other structure of the brain that is highly layered, containing billions of neurons, also having white and gray regions. The gray matter in these layers is composed of neuronal cell bodies, the white matter consists of axons and glial cells. Finally, axons may project from one cerebral hemisphere to the other in bundles that are called commissures. The largest of these interhemispheric projections is the main commissure crossing the hemispheres called the corpus callosum.

How does the brain get its blood supply?

The brain needs oxygen and energy, which its extracts from blood. Two sets of arteries bring blood to the brain: the vertebral arteries, which supply blood to the caudal portion of the brain, and the internal carotid arteries, which supply blood to wider brain regions. The primary purpose of increased blood flow is not to increase the delivery of oxygen and glucose to the active tissue, but rather to hasten removal of the resultant metabolic by-products of the increased neuronal activity.

A guided tour of the brain

The spinal cord

The spinal cord takes in sensory information from the body's peripheral sensory receptors, relays it to the brain, and conducts the outgoing motor signals from the brain to the muscles. The spinal cord runs from the brainstem at about the first spinal vertebra to its termination in the cauda equina. It is enclosed in the bony vertebral column that extend from the base of the skull to the fused vertebrae at the coccyx (tailbone). 

The brainstem: medulla, pons, cerebellum and midbrain

We usually think of the brainstem as having three main parts: the medulla, the pons and the cerebellum, and the midbrain. The brainstem contains groups of motor and sensory nuclei, nuclei of widespread modulatory neurotransmitter systems, and white matter tracts of ascending sensory information and descending motor signals. 

The brainstems most caudal region is the medulla, which is continuous with the spinal cord. It houses the cell bodies of 12 cranial nerves, providing sensory and motor innervations to the face. Functionally, the medulla is a relay station for sensory and motor information between body and brain, it is the crossroads for most of the body's motor fibers. 

The pons is latin for 'bridge' and it is named that way because it is the main connection between the brain and the cerebellum. The pons is important for some eye movement as well as movements of the face and mouth. The reticular formation as three colomns of nuclei: raphe nuclei, parvocellular reticular nuclei, gigantocellular nuclei. 

The cerebellum clings to the brainstem at the level of the pons. Most of the fibers arriving at the cerebellum project to the cerebellar cotex, conveying information about motor outputs and sensory inputs describing body position. 

The midbrain lies superior tot he pons and can only be seen in medial view. Large fiber tracts course through the midbrain's ventral region from the forebrain to the spinal cord, cerebellum and other parts of the brainstem. The midbrain also contains some of the cranial nerve ganglia and the superior and inferior colliculus - they play a important role in perceiving objects and locating and orienting towards auditory stimuli. 

The Diencephalon: thalamus and hypothalamus

The thalamus is almost exactly in the center of the brain and perched on top of the brainstem. It is divided in two parts: one in the right hemisphere and one in the left - that straddle the third ventricle. The thalamus has been referred to as the 'gateway to the cortex' because all of the sensory (except the olfactory nerve) modalities make synaptic relays in the thalamus before continuing to the primary cortical sensory receiving areas. 

The main link between the nervous system and the endocrine system is the hypothalamus, which is the chief site for hormone production and control. It lies on the floor of the third ventricle. The hypothalamus controls the functions necessary for maintaining the normal state of the body: basal temperature and metabolic rate, glucose levels, hormonal state, sexual phase, cicadian cycle etc. It accomplishes much of this work through the endocrine system via control of the pituitary gland. The hypothalamus produces hormones as well as factors that can regulate those hormones. 

The telencephalon: cerebrum

The telencephalon develops into the cerebrum which includes most of the limbic system's structures, the basal ganglia, the olfactory bulb, and the cerebral cortex - covering it all. WIllis observed that the brainstem appeared to sport a cortical border encircling it. The classical limbic lobe is made up of the cingulate gyrus of cerebral cortex that extends above the corpus callosum in the anterior-posterior direction and spans both the hypothalamus, the anterior thalamic nuclei, and the hippocampus (memory system).

MacLean named it the limbic system when he suggested to include the amygdala into the group, this is anterior to the hippocampus. The structures included in the limbic system are tightly interconnected with many distinct circuits and share the characteristic that they are the most capable of plasticity in the cortex. 

The basal ganglia are a collection of nuclei bilaterally located deep in the brain beneath the anterior portion of the lateral ventricles, near the thalamus. They include: the caudate nucleus, putamen, globus pallidus, subthalamic nucleus and substantia nigra. The caudate nucleus and the putamen together are known as the striatum. 

What holds the cerebral cortex?

The cerebral cortex is the outermost tissue of the cerebrum. The cerebral cortex sits over the top of the core structures that we have been discussing the last few paragraphs. The folds of the human cortex serve two important functions:

1. They enable more cortical surface to be packed into the skull, if the human cortex were smoothed out to resemble that of a rat, humans would need to have very large heads. 

2. Having a highly folded cortex brings neurons that are located at some distance from each other along the cortical sheet into closer three-dimensional relationships. The axons that make the long-distance corticocortical connections run under the cortex through the white matter and do not follow the foldings of the cortical surface in their paths, so they project directly tot he neurons brought closer together because of the folding. 

The cerebral cortex can be divided by four main divisions: the frontal, parietal, temporal and occipital lobe. The central sulcus divides the frontal lobe from the parietal lobe, and the Sylvian (lateral) fissure separates the temporal lobe from the frontal and parietal lobe. 

How do you divide the cortex by cell architecture?

Cytoarchitectionics uses the microanatomy of cells and their organizations to subdivide the cortex. The cortex can now be divided in almost 200 defined areas. We use the Brodmann system to number the system and anatomical names for the cerebral cortex. This often seems very unsystematic, but the numbering has more to do with the order in which Brodmann sampled a region than with any meaningful relations between areas that may or may not exist. 

When using microscopic anatomical criteria, it is also possible to subdivide the cerebral cortex according to the general patterns of the cortical layers. 90% of the cortex is composed of neocortex - cortex that contains six cortical layers or that passed through a developmental stage involving six cortical layers. The mesocortex is a term for the so-called paralimbic system. 

How do you divide the cortex by function?

The different lobes in the cerebral cortex have a variety of functional roles in neural processing. Typically, cognitive brain systems are composed of networks whose component parts are located in different lobes of the cortex. 

• The frontal lobe has two main functional subdivisions; the prefrontal cortex and the motor cortex. It receives input from the cerebellum and basal ganglia via the thalamus and the premotor area. It is mainly responsible for generating neural signals that control movement. The motor association areas modulate inhibition, planning and sensory guidance. 

• The parietal lobe receives sensory information about touch, pain, temperature sense and limb proprioception via the receptor cells on the skin.

• The specific cortical regions of the somatosensory and motor cortices that process the sensations and motor control of specific parts of the body have been mapped out. The mapping of specific parts of the body to specific areas of the somatosensory cortex is known as somatotopy - but these maps are not set in stone and do not have necessarily distinct borders. 

• The occipital lobe is related to vision. The visual information from the outside world is processed by multiple layers of cells in the retina and transmitted via the optic nerve to the lateral geniculate nucleus of the thalamus. 

• Neural projections from the cohclea (auditory sensory organ in the inner ear) proceed through the subcortical relays to the medial geniculate nucleus of the thalamus and then tot the primary auditory cortex. The auditory cortex has a tonotopic organization which means that the physical layout of the neurons is based on the frequency of sound. 

• A good portion of the neocortex that is netiher primary sensory cortex nor primary motor cortex is traditionally been termed as association cortex

• The more anterior region of the frontal lobe, the prefrontal cortex, is the last to develop and is evolutionary the youngest region of the brain. It is therefor also proportionately larger in humans compared to the brain of other primates. The main regions are: the dorsolateral PFC, the ventrolateral PFC, the orbitofrontal cortex and the medial PFC. It takes part in the more complex aspects of planning, organizing, controlling and executing behavior, also known as the executive functions. 

• The paralimbic ares form a belt around the basal ganglia and medial aspects of the cerebral hemispheres and don't reside in a single lobe. Processing in these areas provides critical information about the relevance of a stimulus for behavior, rather than just its physical characteristics, which are provided by the sensory areas. 

The advantage we have over other primates is that our brains are larger in absolute volume and weight; therefore, we have more neurons. In addition to neuron number, other aspects of brain structure might affect cognitive ability. But the number of neurons that an average neuron connects to actually does not change with increasing brain sizes. By maintaining absolute connectivity, not proportional connectivity, larger brains became less interconnected. But evolution came up with two clever solutions:

1. Minimizing connection lengths: short connections keep processing localized, with the result that the connection costs are less. Shorter axons take up less space, less energy is required for building and signaling is faster over shorter distance. 

2. Retaining a small number of very long connections between distant rites: primate brains in general and human brains in particular have developed what is known as 'a small-world' architecture. It combines very short, fast local connections with a few long-distance connections to communicate the results of local processing. This design allows both a high degree of local efficiency and, at the same time, quick communication to the global network. 

How does the development of the nervous system look like?

Fertilization of the egg is followed by a series of events that lead to the formation of a multicellular blastula, that is already begun to specialize. The early processes that go into forming the nervous system are called neurulation. As the nervous system continues to develop, the cells at the lateral borders of the neural plate push upwards. This causes the more central cells of the neural plate to invaginate to form the neural groove. As the groove deepens the cells form the neural tube.

At the end of 6 weeks, when there is a stockpile of cells, asymmetrical division begins. After every cell division, one of the two cells formed becomes a migratory cell destined to be part of another layer.

A host of behavioral changes takes place during the first months and yeard of life. Although the brain nearly quadruples in size from birth to adulthood, the change is not due to an increase in neuron number. A substantial amount of that growth comes from synaptogenesis - the formation of synapses, and the growth of the dendrites. At roughly the same time as the synaptogenesis the neurons in the brain are increasing the size of their dendrites. The synaptogenesis is followed by the synapse elimination, or pruning. The person you become is shaped by the growth and elimination of the synapses, which in turn are shaped by the world you're exposed to and the experiences you have. 

How did the investigation into hemispheric specialization start?

For centuries, the effects of unilateral brain damage have revealed major functional differences between the two hemispheres. The most dramatic and most studied has been the effect of the left-hemisphere damage on language functions. 

The major lobes (frontal, parietal, occipital and temporal) appear, at last superficially, to be symmetrical, and each half of the cerebral cortex of the human brain has approximately the same size and surface area. The two hemispheres are offset, however. The right protrudes in front, and the left protrudes in back. Anatomists of the 19th century found that the Sylvian fissure - the large sulcus that defines the superior border of the temporal lobe - has a more prominent upward curl in the right hemisphere than it does in the left hemisphere, where it is flat. Geschwind measured the temporal lobe and came to the conclusion that the planum temporale, around Wernicke's area, was larger in the left hemisphere. 

The asymmetry of the planum temporale is one of the few examples in which an anatomical index is correlated with a well-defined functional asymmetry. By studying the cellular basis of hemispheric specialization, we seek to understand whether differences in neural circuits between the hemispheres might underlie functional asymmetries in tasks such as language. A promising approach is to look for specializations in cortical circuitry within homotopic areas - such as differences in the cortical microcircuitry between the two hemispheres both anterior and posterior. 

Additional structural differences have been documented in both anterior and posterior language cortex. These asymmetries include cell sizes differences between the hemispheres. Cortical areas have a basic underlying organization, documenting cortical locations involved in certain functions should be distinguished in terms of form and variety, between the neural structures common to all regions and the structures critical for a region to carry out particular cognitive functions. 

What is the anatomy of communication?

The corpus callosum and the commissures

The left and right cerebral hemispheres are connected by the largest white matter structure in the brain (the corpus callosum) and the two much smaller fiber tracts (the anterior and posterior commissures). The corpus callosum is divided on macroscopic level into the genu, the body and the splenium. The splenium is the most posterior portion of the corpus callosum. When the posterior half of the callosum is sectioned in humans, the transfer of visual, tactile and auditory sensory information is severely disrupted. By using the diffusion tensor imaging (DTI) technique researchers have traced the white fiber tracts from one hemisphere across the corpus callosum to the other hemisphere. The corpus callosum can be partitioned into vertical segments carrying homotopic connections - those that go into the corresponding region in the other hemisphere - and heterotopic connections - those that travel to a different region in the other hemisphere. 

The callosal fibers also connect heterotopic areas. These are regions with different locations in the two hemispheres. These projections generally mirror the ones found within a hemisphere. The anterior commissure is a much smaller band of fibers connecting the two hemispheres, including the two amygdalae. The posterior commisssure is even smaller and also carries some interhemispheric fibers. 

What is the function of the corpus callosum?

The corpus callosum is the primary highway between the two cerebral hemispheres, and people want to know how and what exactly is being transported between the two hemispheres. In young developing humans and animals callosal projections are diffuse and more evenly distributed across the cortical surface. Cats and monkeys, for instance, lose about 70% of their callosal axons during development. But the reason axon loss doesn't lead to cell loss in both hemispheres is that a signal cell body can send out more than one axon terminal. 

The difference in some corpus callosum sizes may also be attributed to differences in brain size. For instance, the size of the corpus callosum is bigger in men than women. 

Can you split the brain? Cortical disconnection

Myers and Sperry did some experiments with animals to assess whether the corpus callosum was crucial for unified cortical function. They first trained the cats to choose a 'plus' stimulus versus a 'circle' stimulus. Then they made the discovery that when the corpus callosum and anterior commissure were sectioned, such visual discriminations learned by one hemisphere did not transfer to the other hemisphere. 

Corpus callosotomy, or split-brain surgery, is used to treat intractable epilepsy when other forms of treatment, such as medication, fail to function. The first time this was executed, it was done by a professor in NY, named Van Wagenen. To everyone's relief, the surgery was a great success. The patient appeared and felt completely normal. The main method of testing the perceptual and cognitive functions of each hemisphere has changed little over the past 50 years. The ability to communicate solely to one hemisphere is based on the anatomy of the optic nerve. When you look at an object in front of you, information from the right side of you visual field hits the left side of the retina (both eyes), and information from the left side of your visual field hits the right side of the retina. 

There are a number of methodological issues that arise in evaluations of the performance of split-brain patients:

1. Bear in mind that these patients were not neurologically normal before their callosotomy. Therefore it is unreasonable to ask whether they provide an appropriate barometer of noral hemispheric function after the operation. 

2. It is also important to consider whether the transcortical connections were completely sectioned, or whether some fibers remained intact. 

3. Experiments must be meticulously designed to eliminate the possibility of cross-cuing, which occurs when one hemisphere initiates a behavior that the other hemisphere detects externally, giving it a cue about the answer to a test. 

When the corpus callosum is fully sectioned, little or no perceptual or cognitive interaction can occur between the two hemispheres. Surgeons therefor sometimes perform the split-brain procedure in stages, first the anterior or posterior part of the corpus callosum. The remaining fibers are sectioned in a second operation only if the seizures continue to persist. 

When the posterior half of the callosum is sectioned, transfer of visual, tactile, and auditory sensory information is severely disrupted, but the remaining intact anterior region of the callosum is still able to transfer higher-order information. 

What is the evidence of lateralized brain functions from split-brain patients?

When you want to understand the neural bases of language, it is useful to distinguish between grammatical and lexical functions. Grammar is the rule-based system that humans have for ordering words to facilitate communication. The lexicon is the dictionary of the mind, where words are associated with specific meanings. The grammar-lexicon distinction is more apparent when you are learning a new language. You often learn stock phrases that you speak as a unit rather than struggling with the grammar. 

Language and speech are rarely present in both hemispheres; they are either in one or the other. The left hemisphere normally comprehends all aspect of language, the right hemisphere does have linguistic capabilities, although they are uncommon. Both hemispheres also show a word superiority effect. This means that people are better able to identify letters in the context of a real word, than in the context of a pseudoword. In sum, there appear to be two lexicons, one in each hemisphere. 

What is visuospatial processing?

Early testing made it clear that the two hemispheres have different visuo-spatial capabilities. The right hemisphere is specialized for efficiently detecting upright faces and discriminating among similar faces. The left hemisphere is not good at distinguishing among similar faces, but is able to distinguish among dissimilar ones when it can tag the feature differences with words. Both hemispheres can generate spontaneous facial expressions, but you need your left hemisphere to produce voluntary facial expressions. When a split-brain patient gives it left hemisphere the command to smile, the lower-right side of the face responds first, while the left side responds about 180 ms later. Why does it respond at all? Most likely, the signal is rerouted through secondary ipsilateral pathways that connect to both facial nuclei, which then eventually send the signal over to the left-side facial muscles. So, the left hemisphere can trigger voluntary facial expressions, but both hemispheres can trigger involuntary expressions. 

What is the interaction of attention and perception?

After cortical disconnection, perceptual information is not shared between the two cerebral hemispheres. We noted earlier that split-brain patients cannot integrate visual information between the two visual fields. The same is true for certain types of somatosensory information presented to each hand. Thus, when holding an object in the left hand, a split-brain patient is unable to find an identical object with the right hand. Experiments showed that spatial attention can be directed with ease to either visual fields, and this raised the question of whether each separate cognitive system in the split-brain patient, if instructed to do so, could independently and simultaneously direct attention to a part of its own visual field. Some forms of attention are integrated at the subcortical level, and other forms act independently in the separated hemispheres. Split-brain patients can use either hemisphere to direct attention to positions in either the left or right visual field. 

The interpreter

A hallmark of human intelligence is that it is our ability to make causal interpretations about the world around us. For instance, when you walk outside and see a gray sky and a wet ground you probably automatically assume that it has rained. Even though you did not witness the rain and also nobody told you it had rained. A large part of the right hemisphere's impoverishment can be attributed to the finding that causal inferences and interpretations appear to be a specialized ability of the left hemisphere. The left hemisphere appears to have a specialized ability to make causal inferences and form hypotheses. This unique specialization of the left hemisphere is also called interpreter.

A typical observation occurs when the speaking left hemisphere offers some kind of rationalization to explain actions that were initiated by the right hemisphere but were spurred on by a motivation unknown to the left hemisphere. For example, when a split-brain patient was getting a command to stand up, only available to the right hemisphere, the patient stood up. When asked the patient why he was getting up the left hemisphere immediately came up with a plausible explanation: ''I felt like getting a coke''. If the corpus callosum would be intact, the patient would have responded that he stood up because that was the instruction he had received. When predicting which of the two events will occur, the left hemisphere uses a frequency-matching strategy, where-as the right hemisphere uses a maximizing strategy. The left hemisphere is also better at making causal inferences, but the right one is better at judgments of causal perception. 

What is the evidence of lateral brain functions, comparing the normal and malfunctioning brain?

Researchers have also designed experiments to test the differential processing of the two hemispheres in people with intact brains. Studies of auditory perception similarly attempt to isolate the input to one hemisphere. As in vision work - the stimuli can be presented monaurally - that is, restricted to one ear. An alternative methodology for isolating the input is the dichotic listening task. In this task two competing messages are presented simultaneously, one to each ear, and the participant tries to report both messages. But there are some limitations to this kind of studies:

• The effects are small and inconsistent, perhaps because healthy people have two functioning hemispheres connected by an intact corpus callosum that transfers information quite rapidly. 

• There is an bias in the scientific review process towards publishing papers that find significant differences over papers that report no differences. It is much more exciting to report asymmetries in the way we remember lateralized pictures of faces than to report that effects are similar.

• Interpretation is problematic. What can be inferred from an observed asymmetry in performance with lateralized stimuli? 

How do you map functional and anatomical connectivity?

Researchers can also use fMRI techniques to explore hemispheric differences in healthy individuals. On measuring the functional connectivity of brain regions within the same hemisphere and between the two hemispheres, they found that the left and right hemispheres had different patterns of functional connectivity. Neurologically healthy participants exhibit a right-ear advantage when performing the dichotic listening task. When listening to songs, however, while there is a right-ear advantage for the song's words, there is a left-ear advantage for the melodies of the songs. 

What is the evolutionary basis of hemispheric specialization?

In this chapter we have reviewed general principles of hemispheric specializations in humans. Because of the central role of language in hemispheric specialization, laterality research has focused primarily on humans. But the evolutionary pressures that underlie hemispheric specialization would also be potentially advantageous to other species. Humans show handedness, favoring either the left or right hand, dogs and cats show pawedness. But males and females show opposite preferences. Males favor their left paws and females favor their right paws. 

What are the computational problems in object recognition?

When you think about object recognition, there are a few things to keep in mind:

1. Use terms precisely: When you talk about certain cases or patients it is very important for researchers to be precise about when using terms like perceive or recognize. 

2. Object perception is unified: our sensory system uses a divide-and-conquer strategy, but the perception of objects is unified. Features like color and motion are processed along distinct neural pathways. Perception, however, requires more than simply perceiving the features of objects.

3. Perceptual capabilities are enormously flexible and robust: The city vista looks the same whether the view of both eyes or with only the left or the right eye. The percept of an image always stays the same, even if we stand on our head and the retinal image is inverted. 

4. The product of perception is immediately interwoven with memory: object recognition is more than linking features to form a coherent whole. Part of memory retrieval is recognizing that things belong to certain categories.  

Object constancy refers to our amazing ability to recognize an object in countless situations. When you show a drawing of a car, from a different view each time, a person has no problem identifying the object in each picture as a car, and discerning that all four cars are the same model. The visual information emanating from an object varies as a function of three factors: viewing position, illumination conditions, and context. 

1. Viewing position: sensory information depends highly on your viewpoint, which changes not only as you view an object from different angles, but also when the object itself moves and thus changes its orientation relative to you. The human perceptual system is adept at separating changes caused by shifts in viewpoint from changes intrinsic to an object itself. The sensory system automatically uses any sensory cues and past knowledge to maintain object constancy. 

2. Illumination: while the visible parts of an object may differ depending on how light hits it and where shadows are cast, recognition is largely insensitive to changes in illumination. A dog in the sun and a dog in the shade both register as a dog.

3. Context: objects are rarely seen in isolation. People see objects surrounded by other objects and against varied backgrounds. Yet we have no trouble separating, for instance, a dog from other objects on a crowded city street. Our perceptual system quickly partitions the scene into components. 

Object recognition must accommodate these three sources of variability. But the system also has to recognize that changes in perceived shape may reflect actual changes in the object. 

What are the multiple pathways for visual perception?

The pathways carrying visual information from the retina to the first few synapses in the cortex segregate into multiple processing streams. Much of the information goes to the V1 (primary visual cortex). Output from the V1 is contained primarily in two major fiber bundles, which carry visual information to regions of the parietal and temporal cortex - that are involved in visual object recognition. 

There is the ventral (occipitotemporal) stream and the dorsal (occipitoparietal) stream. These two are also known as the what and where pathways. Ungerleider and Mishkin proposed hat processing along these two pathways is designed to extract fundamentally different types of information. 

They hypothesized that the ventral stream is specialized for object perception and recognition, for determining 'what' we are looking at. The dorsal stream is specialized for spatial perception, for determining 'where' an object is, and for analyzing the spatial configuration between different objects in a scene. What and where are two basic questions to be answered in visual perception. To be more specific, the dorsal stream or 'where' is going upwards from the back of the brains to the front, the ventral stream is 'what' and is going downwards from the back of the brain to the front. If you want to use a mnemonic; dorsal comes first in the alphabet when you choose between dorsal and ventral, so dorsal is above and ventral is below.

The first data for the what-where dissociation of the ventral and dorsal stream comes from animal studies. Animals with bilateral lesions to the temporal lobe that disrupted the ventral stream had great difficulty discriminating between different shapes (the 'what' discrimination). But, these animals had no problems determining where the object was in relation to other objects, because this second ability depends greatly on the 'where' route. But the separation of the 'what' and 'where' routes is not limited to the visual system, for instance in audition. 

What are the representational differences between the dorsal and ventral streams?

Neurons in both the temporal and parietal lobes have large receptive fields, but the physiological properties of the neurons within each lobe are quite distinct. 40% of these neurons have receptive fields near the central region of vision, the remaining cells have receptive fields that exclude the foveal region. These eccentrically tuned cells are ideally suited for detecting the presence and location of a stimulus, especially one that has just entered the field of view. 

The response for neurons in the ventral stream of the temporal lobe is quite different. The receptive fields for these neurons always encompass the fovea, most of these neurons can be activated by a stimulus that falls within either the left or the right visual field. Cells within the visual areas of the temporal lobe have a diverse pattern of selectivity. In the posterior region cells show a preference for relatively simple features such as edges. Further along the process stream, they have a preference for much more complex figures; such as human body parts, apples, flowers or snakes etc. 

What is the difference between perception for identification and perception for action?

Agnosia is an inability in processing sensory information even though the sense organs and memory are not defective. To be agnosic means to experience a failure of knowledge or recognition of objects, persons, shapes, sounds, or smells. When the disorder is limited to the visual modality, is it referred to as visual agnosia. This is a deficit in recognizing objects even when the processes for analyzing basic properties such as shape, color, and motion are relatively intact. 

Patient DF is an extraordinary case. She couldn't name the right household items, made errors in labeling them. She usually gave crude descriptions of displayed objects. Picture recognition was even more disrupted. When DF was given an explicit matching task she failed miserably. She couldn't orientate the card the right way for fitting the lock. But when she was asked to insert the card into the slot, DF quickly reached forward and inserted the card into the lock. The explicit matching task couldn't succeed because DF could not recognize the orientation of the object because of the severe agnosia. But when DF was asked to insert the card, the shape and orientation information were available for the visuomotor task. So, the 'where' system appears to be essential for more than determining the locations of different objects; it is also critical for guiding interaction with these objects. 

So, patients with selective lesions in the ventral pathway may have severe problems in consciously identifying objects, yet they can use the visual information to guide coordinated movement. Thus we see that visual information is used for a variety of purposes. 

Optic ataxia holds that patients can recognize objects, yet they cannot use visual information to guide their actions. When someone with optic atraxia reaches for an object, she doesn't move directly toward it; rather, she gropes about like a person trying to find something in the dark. Optic atraxia is associated with lesions in the parietal cortex.

How do you see shapes and perceive objects?

Object perception depends primarily on an analysis of the shape of a visual stimulus, though cues such as color, texture and motion certainly also contribute to normal perception. But, even when the surface features are absent or applied inappropriately (think about an abstract painting), we are still able to recognize the object using perceptual ability to match the analysis of shape and form to an object, regardless of color, texture, or motion cues. 

One way to investigate how we encode shapes is to identify areas of the brain that are active when we compare contours that form a recognizable shape versus contours that are just squiggles. There is an idea that perception involves a connection between sensation and memory in the brain. Researchers explored this question using a PET study designed to isolate the specific mental operations used when people viewed familiar shapes, novel shapes, or stimuli formed by scrambling the shapes to generate random drawings. Viewing both novel and familiar stimuli led to increases in regional cerebral blood flow bilaterally in lateral occipital cortex (LOC). Many others have also shown that the LOC is critical for shape and object recognition. People have an insensitivity to the specific visual cues that define an object, this is known as cue invariance. Thus, the LOC can support the perception of an elephant even when the elephant is blue and green, or an apple shape even when the apple is made of onyx and striped. 

The functional specification of the LOC can also be tested with 6-month-old babies. To do this researchers use a fNIRS, functional near-infrared spectroscopy, which employs a lightweight system that looks similar to an EEG cap and can be comfortably placed on the infant's head. This system uses infrared light, that can project through the head and skull. The repetition suppression (RS) effect is hypothesized to indicate increased neural efficiency: the neural response to the stimulus is more efficient and perhaps faster when the pattern has been recently activated. 

From shapes to objects

Multistable perception is an image where their is an object that you can see in a black-and-white view, such as a vase, but when you point your attention to another part of the image you see a different object. The vase can change profiles in two people facing each other, an then you can go back to the vase, back to the two people, on and on. This is an example of multistable perception. The stimulus information does not change at the points of transition from one percept to the other, but the interpretation of the pictorial cues does. 

What is the role of the grandmother cell in ensemble coding?

How do we recognize specific objects? Are there individual cells that respond only to specific integrated percepts, or does perception of an object depend on the firing of a collection or ensemble of cells? In the latter case, this would mean that when you see a peach, a group of neurons that code or different features of the peach might become active, with some subset of them also active when you see a nectarine. A type of neuron that can recognize a complex object is called a gnotic unit, referring to the idea that the cell signals the presence of a known stimulus - an object, a place, or an animal that has been encountered in the past. 

Researchers also discovered cells in the IT gyrus and the floor of the superior temporal sulcus (STS) that are selectively activated by faces. They coined the term grandmother cell to convey the notion that people's brains might have a gnostic unit that becomes excited only when their grandmother comes into view. Although it is tempting to conclude that there are cells like this that are gnostic units, it is important to keep in mind the limitations of such experiments:

• Aside from the infinite number of possible stimuli, the recordings are performed on only a small subset of neurons. This cell potentially could be activated by a broader set of stimuli, and many other neurons might respond in a similar manner.

• The results also suggest that these gnostic-like units are not really 'perceptual'. The cell could represent a concept of, for instance, a 'grandmother'.

One alternative to the grandmother-cell hypothesis is that object recognition results from activation across complex feature detectors. Granny, then, is recognized when some of these higher-order neurons are activated. According to this ensemble hypothesis, recognition is not due to one unit but to the collective activation of many units. 

What are the top-down effects of object recognition?

Up to this point, we have emphasized a bottom-up perspective on processing within the visual system, showing how a multilayered system can combine features into more complex representations. This model appears to nicely capture the flow of information along the ventral pathway. But there is also an top-down way we are not forgetting. One model of top-down effects emphasizes that input from the frontal cortex can influence processing along the ventral pathway. The frontal lobe generates predictions about what the scene is, using this early scene analysis and knowledge of the current context. These top-down predictions can then be compared with the bottom-up analysis occurring along the ventral pathway of the temporal cortex, making for faster object recognition by limiting the field of possibilities. 

Can you read minds?

We have seen various ways in which scientists have show us that you can manipulate the output and input of the visual cortex. These observations have led investigators to realize that it should, at least in principle, be possible to analyze the system in the opposite direction. That is, we should be able to look at someone's brain activity and infer what the person is currently seeing - a form of mind reading. This idea is referred to as decoding: the brain activity provides the coded message, and the challenge is to decipher it and infer what is being represented. 

There are two issues:

1. Our ability to decode mental states is limited by our models of how the brain encodes information.

2. Our ability to decode will be limited by the resolution of our measurement systems. 

How does the specificity of object recognition in higher visual areas work?

When we meet someone, we always look at that person's face. The face, particularly the eyes, of another person can provide significant cues about what is important in his environment. Also, looking at someone's lip when they are speaking can provide a lot more information about what that person is saying. 

Is face processing special?

It seems reasonable to suppose that our brains have a general-purpose system for recognizing all sorts of visual inputs, with faces constituting just one important class of problems to solve. But multiple studies argue that face perception does not use the same processing mechanisms as those used in object recognition, but instead depends on a specialized network of brain regions. Do the processes of face recognition and nonfacial object recognition involve physically distinct mechanisms? Although clinical evidence showed that people could have what appeared to be selective problems in face perception, more compelling evidence of specialized face perception mechanims comes from neurophysiological studies with nonhuman primates. Neurons in various areas of the monkey brain show selectivity for face stimuli. 

The similar specificity for faces is observed using fMRI studies in humans, including an area in the right fusiform gyrus parahippocampal place area (PPA). This area is specialized for processing information about spatial properties, for instance the difference between an indoor and outdoor scene, and the extrastriate body area (EBA) and the fusiform body area (FBA) have been identified as more active when body parts are viewed. 

What are failures in object recognition?

Patients with visual agnosia have provided a window into the processes that underlie object recognition. By analyzing the subtypes of visual agnosia and their associated deficits, we can draw inferences about the processes that lead to object recognition. Although the term visual agnosia has been applied to a number of distinct disorders associated with different neural deficits, patients with visual agnosia generally have difficulty recognizing objects that are presented visually or require the use of visually based representations. 

The current literature broadly distinguishes between three major subtypes of visual agnosia: apperceptive, integrative and associative. 

1. Apperceptive visual agnosia: The recognition problem is one of developing a coherent percept: the basic components are there, but they can't be assembled. It's somewhat like going to Legoland, but instead of seeing buildings, cars, and monsters, you can only see piles of Lego bricks. The elementary visual functions - acuity, colorvision, and brightness - are still intact. The object recognition problems become especially evident when a patient is asked to identify objects on the basis of limited stimulus information, for instance when the object is shown as a line drawing or is seen from an unusual perspective. 

2. Integrative visual agnosia: this is a subtype of the apperceptive visual agnosia, where people perceive the parts of an object but are unable to integrate them into a coherent whole. At Legoland they may see walls and windows, but not a house. A patient's object recognition problems became apparent when he was asked to identify objects that overlapped each other. 

3. Associative visual agnosia: perception occurs without recognition. It is the inability to link a percept with its semantic information, such as its name, properties or functions. A patient can perceive objects with het visual system but cannot understand them or assign meaning to them. At Legoland she may perceive a house, and be able to draw a picture of that house, but still be unable to tell that it is a house or describe what a house is for. 

Patients with agnosia are unable to recognize common objects. This deficit is modality specific. Patients with visual agnosia can recognize an object when they touch, smell, taste or hear it, but not when they can only see it. Therefor, visual agnosia can be category specific. Category-specific deficits are deficits of object recognition that are restricted to certain classes of objects. Linked to this there has been a debate in research about how object knowledge is organized in the brain. One theory suggests that it is organized by features and motor properties, and the other suggests specific domains relevant to survival and reproduction. 

What is prosopagnosia?

Prosopagnosia is the term used to describe an impairment in face recognition. Given the importance of face recognition, propsopagnosia is one of the most fascinating and disturbing disorder of object recognition. Propsopagnosia is usually observed in patients who have lesions in the ventral pathway, especially occiptial regions associated with face perception and the fusiform face area. Some patients also have congenital propsopagnosia (CP), defined as a lifetime impairment in face recognition that cannot be attributed to a known neurological condition. 

Hostilic processing is a form of perceptual analysis that emphasizes the overall shape of an object. This mode of processing is especially important for face perception. We can recognize a face by the overall configuration of its features, and not by the individual features itself. 

Analysis-by-parts processing is a form of perceptual analysis that emphasizes the component parts of an object. This mode of processing is important for reading, when we decompose the overall shape into its constituent parts.

What holds the anatomy and control of motor structures?

To understand motor control, we have to consider the organization and function of much of the dorsal territory of the cerebral cortex, as well as much of the subcortex. The lowest level of the hierarchy centers on the spinal cord. Axons from the spinal cord provide the point of contact between the nervous system and muscles, with incoming sensory signals from the body going to ascending neurons in the spinal cord, and outgoing motor signals to the muscles coming from descending spinal motor neurons. At the top of the hierarchy are cortical regions that help translate abstract intentions and goals into movement patterns. Between the association areas and the spinal cord sit the primary motor cortex and brain structures, which with the basal ganglia and cerebellum, convert these patterns into commands to the muscles. 

What are the roles of muscles, motor neurons and the spinal cord?

Action, or motor movement, is generated by stimulating skeletal muscle fiber of an effector. An effector is a part of the body that can move. All forms of movement result from changes in the state of muscles that control an effector or group of effectors. Muscles consist of elastic fibers, tissue that can change in length and tension and are activated by motor neurons, which are the final neural elements of the motor system. Alpha motor neurons innervate muscle fibers and produce contractions of the fibers. Input to the alpha motor neurons comes from a variety of sources. Alpha motor neurons receive peripheral input from muscle spindles, sensory receptors embedded in the muscles that provide information about how much the muscle is stretched. 

The axons of the spindles form an afferent nerve that enters the dorsal root of the spinal cord and synapses on spinal interneurons that project to alpha motor neurons. Reflexes allow postural stability to be maintained without any help from the cortex. 

What are the subcortical motor structures?

There are 12 cranial nerves, essential for critical reflexes associated with breathing, eating, eye movements, and facial expressions that originate in the brainstem. The substantia nigra sends out direct projections down the spinal cord. This motor pathway is referred to as the extrapyramidal tract, meaning that this is not a part of the pyramidal part, the axons that travel directly from the cortex to the spinal segments. The cerebellum is a massive structure containing over 75% of all the neurons in the brain. Damage to the cerebellum from stroke, tumor or degenerative processes results in a syndrome called ataxia. Patients with ataxia have a lot of difficulty maintaining balance and producing well-coordinated movements. 

The basal ganglia is the other major subcortical motor structure next to the cerebellum and substantia nigra. It consists out of a collection of five nuclei: caudata nucleus, putamen, globus pallidus, subthalamic nucleus, and the substantia nigra. I will use the term motor areas to refer to cortical regions involved in voluntary motor functions, including planning, control and execution of movement. 

Which cortical regions are involved in motor control?

The motor cortex regulates the activity of spinal neurons in direct and indirect ways. The corticospinal tract (CST) consists of axons that exit the cortex and project directly to the spinal cord. The CST is also referred to as the pyramidal tract, because the mass of axons resembles a pyramid as it passes through the medulla oblongata. 

The primary motor cortex (M1) is located in the most posterior portion of the frontal lobe, spanning the anterior wall of the central sulcus and extending onto the precentral gyrus. M1 receives input from almost all cortical areas implicated in motor control. M1 includes two anatomical subdivisions: an evolutionairy older rostral region and a more recently evolved caudal region. Corticospinal neurons that originate in the caudal region may terminate on interneurons or directly stimulate alpha motor neurons. The latter known as corticomotorneurons or CM neurons, include prominent projections to muscles of the upper limb, and they support the dexterous control of our fingers and hands. 

The preeminent status of the primary motor cortex for movement control is underscored by the fact that lesions to this area, or to the corticospinal tract, produce a devastating loss of motor control. Lesions of the primary motor cortex usually result in hemiplegia, the loss of voluntary movements on the contralateral side of the body. Reflexes are absent immediately after a stroke that produces hemiplegia. But within a couple of weeks the reflexes return and are frequently hyperactive or even spastic. 

The lateral and medial aspects of Brodmann area 6 are referred to as premotor cortex and supplementary motor area (SMA). The secondary motor areas are involved in planning and control of movements, but they do not accomplish this feat alone. The premotor cortex has a strong reciprocal connection with the parietal lobe. 

The dorso-dorsal stream passes through the superior parietal lobe and projects to the dorsal premotor cortex. This pathway plays a dominant role in one of the most important motor activities: reaching. Patients with lesions in the dorso-dorsal stream have optic ataxia: they are unable to reach accurately for objects, especially those in their peripheral vision. 

The ventro-dorsal stream passes through the inferior parietal lobe and projects to the ventral premotor cotex. This pathway is associated with producing both transitive gestures and intransitive gestures. Lesions along this processing stream can result in apraxia - a condition that affects motor planning, as well as the knowledge of which actions are possible with a given object. 

What are computational issues in motor control?

The spinal cord is capable of producing orderly movement, and the stretch reflex provides an elegant mechanism to maintain postural stability even in the absence of higher-level processing. Sherrington observed by looking at a cat whose spinal cord was disconnected from the spinal apparatus, the cat was still able, without the appropriate stimulus, to make movements like he/she was walking. Thus, neurons in the spinal cord could produce an entire sequence of actions without any descending commands or external feedback signals. These neurons have come to be called central pattern generators. They most likely evolved to trigger actions essential for survival, such as locomotion. 

But if the cortical neurons are not coding specific patterns of motor commands, what are they doing? Researchers did an experiment with monkeys that had been deprived of all somatosensory, or afferent, signals from the limbs. The monkeys were trained to simple point at a light. If, the animal generated a motor command specifying the desired position, it should have achieved this goal once the opposing force was removed. The results show that when the torque motor was on, the limb stayed at the starting location. As soon as it was turned off, the limb rapidly moved to the correct location. This experiment provides evidence that the location isn't the only thing being coded by humans. Although endpoint control reveals a fundamental capability of the motor control system, distance and trajectory planning demonstrates additional flexibility in the control processes. 

What are the hierarchical representations of action sequences?

Hierarchical representational structures organize movement elements into integrated chunks. Researchers originally developed the idea of 'chunking' when studying memory capacity, but it has also proved relevant to the representation of action. So, the motor system is also hierarchically organized. Subcortical and cortical areas represent movement goals at various levels of abstraction. 

What is the physiological analysis of motor pathways?

In this chapter we have stressed two critical points of movement: (1) motor control depends on several distributed anatomical structures, (2) these distributed structures operate in hierarchical fashion. 

Neuropsychologists have long puzzled over how best to describe cellular activity in the motor structures of the CNS. Stimulation of the primary motor cortex, either during neurosurgery or via TMS, can produce discrete movements about single joints, providing a picture of the somatotopic organization of the motor cortex. Research also shows that activity of the cells in the primary motor cortex correlates much better with movement direction than with target location. Many cells in the motor cortex show directional tuning, or exhibit what is referred to as a preferred direction. Directional tuning is not just observed in the primary motor cortex; similar tuning properties are found in cells in premotor and parietal cortical areas, as well as in the cerebellum and basal ganglia. We can assume that activity is distributed across many cells, each with its unique preferred direction. Researchers introduced the concept of population vector: each neuron can be considered to be contributing a 'vote' to the overall activity level. The strength of the vote will correspond to how closely the movement matches the cell's preferred direction: if the match is close, the cell will fire strongly. Thus, the activity of each neuron can be described as a vector, oriented to the cell's preferred direction with a strength equal to its firing rate. 

What are alternative perspectives on the neural representation of movement?

The population vector is dynamic and can be calculated continuously over time. After defining the preferred direction of a set of neurons, we can calculate the population vector from the activation of that set of neurons even before the animal starts to move. This shows that the population vector shifts in the direction of the upcoming movement well before the movement is produced, suggesting that at least some of the cells are involved in planning the movement and not simply recruited once execution of the movement has begun. Even though directional tuning and population vector have become cornerstone concepts in motor neurophysiology, it is also important tot consider that many cells do not show strong directional tuning. Even more puzzling, the tuning may be inconsistent: the tuning exhibited by a cell before movement begins may shift during the actual movement. Researchers are saying that we should take up on a radically different perspective on motor neurophysiology. Rather than viewing neurons as static representational devices, we should focus on the dynamic properties of neurons, recognizing that movement arises as the neurons move from one state to another. 

Although scientist refer to one part of the brain as the motor cortex and one part of the brain as the sensory cortex, we know that these areas are closely intertwined. People produce movements in anticipation of their sensory consequences: we increase the force used to grip and lift in anticipation of the weight we expect to experience. 

How does goal selection and action planning work?

Motor representation are hierarchically and need to encompass the goals of an action in addition to the activation patterns required to produce the movement necessary to achieve those goals. Including sensory information and feedback enables the motor cortex to have more than one option for achieving those goals. 

One hypothesis about how we set our goals and plan action is from Cisek. He says that in incorporates many of the ideas and findings that we are going to look at, providing a general framework for action selection. His affordance competition hypothesis is deeply rooted in an evolutionary perspective. Our ancestors evolved in a world where they engaged in interactions with a changing, and sometimes hostile environment that held a variety of opportunities and demands for action. To survive and reproduce, early humans had to be ever ready, anticipating the next predator etc. Many interaction don't allow time for carefully evaluating plans and goals, considering options: this is called serial processing. 

A better idea is to develop multiple plans in parallel. The affordance competition hypothesis proposes that the processes of action selection and specification occur simultaneously within an interactive neural network, and they evolve continuously. Even when performing one action, we are already preparing the next one. Then there is the competition part. At some point, one option wins out over the other competitors. An action is selected an executed. This selection process involves many parts of the motor pathway, where interactions within frontoparietal circuits have a prominent role. 

There are cells in the premotor cortex that have been shown to represent action goals more abstractly. Some cells are preferentially activated when the animal reaches for an object, other cells become active when the animal makes a gesture to hold an object. 

What are the representational variations across motor areas of the cortex?

The lateral premotor cortex is more heavily connected with the parietal cortex - a finding consistent with the hypothesis that this region plays a role in sensory-guided action. The SMA has strong connections with the medial frontal cortex, and is likely to bias or influence action selection and planning that are based on internal goals and personal experiences. The SMA has also been hypothesized to play an important role in more complex actions, such as those involving sequential movements or those requiring coordinated movements of the two limbs. Damage in the SMA can lead to impaired performance on tasks that require integrated use of the two hands, even though the individual gestures performed by either hand alone are unaffected. Lesions in SMA can also result in alien hand syndrome, a condition in which one limb produces a seemingly meaningful action but the person denies responsibility for the action. 

The lateral premotor cortex is part of a network for stimulus-guided movement, whereas the more medial supplementary motor area is important for movements based on internal goals and personal experience, including skilled movements that require coordination between the two hands. Parietal motor areas also show topography; different regions of the intraparietal cortex are associated with hand, arm, and eye movements. Therefor the parietal motor representations are more goal oriented, whereas premotor-motor representations are more closely linked to the movement itself. The conscious awareness of the movement appears to be related to the neural processing of action intention rather than the movement itself. 

What links are there between action and perception?

The most common known link between perception and action is neurons that are called mirror neurons. These are neurons that are active during action but also active during action perception. You might suppose that the activity in MN's reflects the similar visual properties of the action and perception conditions. Additional experiments ruled out this hypothesis: (1) the same MN that is activated when the monkey cracks a peanut itself is activated when the monkey merely hears a peanut being cracked, (2) MNs are also active when a monkey watches someone reach behind a screen for a peanut but cannot see grasping of the peanut. In fact, there doesn't even need to be a peanut behind the screen, as long as the monkey thinks there's a hidden peanut. The work on a mirror neuron network has revealed the intimate links between perception and action, suggesting that our ability to understand these actions of others depends on the neural structures that would be engaged if we were to produce the action ourselves. 

Coaches and sport psychologists recognize the intimate relationship between action observation an action production. The skier can mentally visualize his movements of the slope. This process is thought to strengthen perception-action links. 

How do you recoupe motor loss?

Lesions to the primary motor cortex or the spinal motor neurons can result in hemiplegia, or in hemiparesis, a unilateral weakness. Such lesions severely impact the patient's ability to use the affected limbs on the contralesional side: unfortunately, these patients rarely regain significant control over the limbs. 

How do you regain movement after loss of motor cortex?

Two critical questions for the clinician and patient are, what is the patient's potential for recovery? what is the best strategy for rehabilitation? A panel looked at biomarkers for predicting motor recovery from stroke. Some biomarkers look promising when the assessment is performed after the patient has recovered from the critical initial post-stroke period, outperforming the location of the lesion and even the behavioral asymmetry between the affected and unaffected limbs. 

The main treatment, traditionally, to regain motor function is physical therapy, a behavioral intervention that seeks to retrain the affected limbs. But physical therapy only produces modest recovery. Also the idea that more therapy is better, has been contradicted with research. A different behavioral method is based on the idea that the brain may favor short-term solutions over long-term gains. Scientists are currently seeking novel interventions that more directly target specific neural mechanisms. 

What is the brain-machine interface?

Can neural signals be used to control a movement directly with the brain, bypassing the intermediate stage of muscles? Could you plan an action in your motor cortex, somehow connect those motor cortex neurons to a computer, and send the planned action to a robot, which would fold the laundry? These systems are called brain-machine interfaces using decoding algorithms to control prosthetic devices with neural signals. 

Brain-machine interfaces are also called BMI's. BMI's offer a promising avenue for rehabilitation of people with mostly severe movement disorders, such as those resulting from, for instance, a spinal cord injury. In the early BMI systems the decoders were built from recordings of neural activity made while the animal produces movements. The output of these decoders was then used to drive the prosthetic device. More recent work has revealed that the brain's plasticity enables it to spontaneously learn how to adapt neural activity to control an arbitrary decoder, eliminating the need for a training phase to build the decoder. This insight is essential if BMI systems will be useful for individuals who have lost the ability to move their limbs by themselves. 

How does movement initiation of basal ganglia work?

When multiple plans are present in the cortex, how do we decide which plan to execute? The basal ganglia plays a critical role in movement initiation. The afferent fibers to the basal ganglia terminate in the striatum, composed in primates of two nuclei: the caudate and the putamen. Processing within the basal ganglia takes place along two pathways that originate with GABAergic projection neurons from the striatum. The direct pathway involves fast, direct, inhibitory connections from the striatum to the basal ganglia. The indirect pathway takes on a slower, roundabout route to the basal ganglia. Stiatal axons inhibit the external segment of the globus pallidus, which in turn inhibits the subthalamic nucleus and GP. The final internal pathway of note is the projection from the pars compacta of the substantia nigra to the striatum, known as the dopamine pathway. The substantia nigra excites the direct pathway by acting on one type of dopamine receptor (D1), and inhibits the indirect pathway by acting on a different type of dopamine receptor (D2). 

When the direct pathway is activated, it sends inhibitory signals to the target neurons in the output nuclei of the basal ganglia, which results in the inhibition of inhibiting signals to the thalamus. This sum effect is disinhibition of the thalamus, resulting in increased excitation of the cortex. So, activation of the direct pathway will promote movement if the disinhibition is along a circuit that terminates in the primary motor cortex. 

Activation along the indirect pathway will result in increased inhibition from the basal ganglia and as such, reduces excitation of the cortex. This puzzling arrangement seems to be an important mechanism for helping the motor system both to maintain stability and to rapidly change when the situation changes. So, the basal ganglia can be seen to play a critical role in the initiation of actions. 

What are disorders of the basal ganglia?

Huntington's disease is a hereditary neurodegenerative disorder. Patients with this gene develop symptoms in the fourth or fifth decade of life, experiencing rapid progression and die within 12 years of onset. Within a year from onset movement abnormalities are noticed: clumsiness, balance problems, and a general restlessness. The excessive movements, or hyperkinesia, can be understand by considering how the pathology affects information flow through the basal ganglia. The striatal changes occur primarily in inhibitory neurons forming the indirect pathway.  

Parkinson's disease is the most common and well-known disorder affecting the basal ganglia, results from a loss of dopamine-producing neurons in the substantia nigra (SN). As with most brain tissue, these neurons atrophy with age. Motor symptoms of Parkinson are related to locomotion called hypokinesia and bradykinesia. Hypokinesia is a reduced ability to initiate voluntary movements, bradykinesia refers to a slowing in the rate of movement. At the extreme end of these symptoms lies akinesia, the total absence of voluntary movement. One of the biggest breakthroughs in neurology occurred with the development of L-dopa, a synthetic precursor of dopamine. But, over time, the dopamine-producing cells continue to die off and striatal neurons become sensitized to L-dopa, so the amount of required medication tends to increase. More recently, the success of invasive techniques such as pallidotomy and deep brain stimulation, where an electrode is placed in the skull to initiate the signal for movement by an Parkinson's disease patient, has inspired neurosurgeons to consider similar interventions for other disorders. 

How do you learn and perform a new skill?

People frequently attribute motor learning to the lower levels of the hierarchical representation of action sequences. We speak of 'muscle memory' as if our muscles have learned how to respond in a way that seems automatic. The fact that we have great difficulty verbalizing how we perform these skills reinforces the notion that learning is noncognitives. 

When people are acquiring new action, the first effects of learning likely will be at a more abstract level. Learning a skill takes practice, and becoming very skilled at anything requires a lot of practice. Our motor system has some basic movement patterns that can be controlled by subcortical circuits. Learning a new skill can involve building on these basic patterns, linking together a series of gestures in a novel way. 

When you come off a boat, you feel that you first few steps are wobbly, it takes a moment or two to become acclimated to the stability of the dock, and to abandon you rolling gait. You sea legs are a form of sensorimotor adaptation. We cannot simply switch back to the normal state, but rather must relearn how to control our limbs in the absence od a visual or force distortion. Sensimotor learning is improvement, through practice, in the performance of motor behavior. The acquisition of a motor skill involves the formation of new movement patterns that can result in changes in both structure and connectivity. 

People have been struggling to define emotion for several thousand years. As a psychological state, emotion has some unique qualities that have to be taken into account. Emotions are embodied, you feel them. They are uniquely recognizable; they are associated with characteristic facial expressions and behavioral patterns of comportment and arousal. Emotions are neurological processes that have evolved to guide behavior in such a manner as to increase survival and reproduction. They improve our ability to learn from the environment and the past. Many researchers claim that a feeling is the subjective experience of the emotion, but not the emotion itself. The most current models posit that emotions are valenced responses (positive/negative) to external stimuli and/or internal mental representations that

• involve changes across multiple response systems

• are distinct from moods, in that they often have identifiable objects or triggers

• can be either unlearned responses to stimuli with intrinsic affective properties, or learned responses to stimuli with acquired emotional value

• can involve multiple types of appraisal processes that assess the significance of stimuli to current goals

• depend of different neural systems

Others agree that emotions involve highly coordinated behavior, body and brain effects, they disagree that these various effects are part of the emotion state. They view them as a result or consequence of the emotion state

• an 'emotion' constitutes an internal, central state

• this state is triggered by specific stimuli

• this state is encoded by the activity of particular neural circuits

• activation of these specific circuits gives rise, in a causal sense, to externally observable behaviors, and to separately associated cognitive, somatic and physiological responses

Emotions fall under the umbrella term of affect, which includes not only discrete emotions that have a relatively short duration, but also more diffuse, longer-lasting states such as chronic stress and mood. Encountering a stimulus or event that threatens us in some way triggers stress, a fixed pattern of physiological and neurohormonal changes. These changes disrupt homeostasis, leading to immediate activation of the sympathetic nervous system's fight-or-flight responses, but also to activation of the hypothalamic-pituitary-adrenal axis and release of stress hormones, such as cortisol. 

A mood is a long-lasting diffuse affective state that is characterized by primarily a predominance of enduring subjective feelings without an identifiable object or trigger. Moods do not have a well-defined neurohormonal or physiological substrate, and the neural correlates of different moods are still poorly understood. 

What are the neural systems that are involved in emotion processing?

The identifying of the neural systems involved in emotion processing is difficult: technical issues with the various methods used to study emotion, controversies over whether emotional feeling, which are subjective, can be studied in humans and animals, and the various interpretations of research findings. 

When emotions are triggered by an external event or stimulus, our sensory system plays a role. The autonome nervous system, or ANS ,is made up of the parasympathetic and sympathetic nervous systems. The two systems work in combination to achieve homeostasis. The ANS is regulated by the hypothalamus, which also control the release of multiple hormones through the HPA axis, made up of the paraventricular nucleus (PVN) of the hypothalamus, the anterior lobe of the pituitary gland, and the cortex of the adrenal glands, which sit above the kidney. Arousal is a critical part of many theories of emotion. The arousal system is regulated by the reticular activating system, which is composed of sets of neurons running from the brainstem to the cortex. 

Papez came up with a circuit that has to do with emotion. The Papez circuit describes the brain areas that James Papez believed were involved in emotion. They include the hypothalamus, anterior thalamus, cingulate gyrus, and hippocampus. The limbic system includes these structures and the amygdala, orbitofrontal cortex, and the portions of the basal ganglia. MacLean proposed that the human brain had three regions that had developed gradually and sequentially over the course of evolution. He used the term limbic system to describe the complex neural circuits involved with the processing of emotion. 

Over the last decades, scientific investigation of emotion has been focused more on human emotion and has also became more detailed and complex. Investigators no longer think there is only one neural circuit of emotion. Rather, depending on the emotional task or situation, we can expect different neural systems to be involved. The neuroimaging approaches based on machine learning revealed that specific emotional states activate several brain networks. 

How do you categorize emotions?

In this section we discuss the basic versus dimensional categorization of emotions. Fearful, sad, anxious, elated, etc. are some of the terms we use to describe our emotional lives. Researchers made up three primary categories:

1. Basic emotions: a closed set of emotions, each with unique characteristics, carved by evolution and reflected through facial expressions

2. Complex emotions: combincations of basic emotions, some of which may be socially or culturally learned, that can be identified as evolved, long lasting feelings

3. Dimensional theories of emotion describe emotions that are fundamentally the same but that differ along one or more dimensions, such as valence and arousal, in reaction to events or stimuli

What are the basic emotions?

There are seven primary-process emotional systems, or core emotional systems, produced by ancient subcortical neural circuits common to all higher animals, which generate both emotional actions and specific autonomic changes that support those actions: SEEKING/desire, RAGE/anger, FEAR/anxiety, LUST/sex, CARE/maternal, GRIEF/seperation distress and PLAY/physiological social engagement. 

For the past 150 years, many investigators of human emotions have considered facial expressions to be one of those predictable changes sparked by an emotional stimulus. Duchenne was the first in doing experiments with facial expressions in a man with facial anesthesia. He electrically stimulated the man's facial muscles and methodically triggered muscle contractions. Duchenne believed that facial expression revealed the underlying emotions. Ekman took up this work and the study of facial expression and came up with the six basic human facial expressions: anger, fear, sadness, happiness, disgust and surprise. Some of the basic emotions have been confirmed in nonhuman mammals, which show dedicated subcortical circuitry for such emotions. 

What are the complex emotions?

Even if we accept that the basic emotions exist, we are still faced with identifying which emotions are basic and which are complex. Jealousy is one of the most interesting of the complex emotions. Also, romantic love is far more complicated than researchers initially thought. These emotions are associated with higher-order cortical areas and are involved with social cognition, theory of mind, and interpretation of actions performed by others. 

Most researchers agree that emotional reactions to stimuli and events can be characterized by two factors: valence (positive and negative) and arousal (high or low). Although, sometimes it is the case that a person feels positive and negative at the same time. By using the dimensional approach - tracking valence and arousal - researchers can be more concretely in assessing emotional reactions elicited by stimuli. So, the dimensional approach, instead of describing discrete states of emotion, describes emotions as reactions that vary along a continuum. 

What are the theories of emotion generation?

Most emotion researchers agree that the response to emotional stimuli is adaptive and that it can be separated into three components. Every theory of emotion generation is an attempt to explain:

• The physiological reaction (racing heart)

• The behavioral reaction (fight-or-flight response)

• The subjective experiential feeling ('I'm scared!')

What the theories don't agree on are the underlying mechanisms, and what causes what. The crux of the disagreement involves the timing of these three components and whether cognition is required to generate an emotional response and subjective feeling or, alternatively, whether an emotional stimulus leads directly to quick automatic processing that results in a characteristic response and feeling.

James-Lange theory of emotion:

James proposed that emotions were the perceptual results of somatovisceral feedback from bodily responses to an emotion-provoking stimulus. A sense organ relayed information about that stimulus to the cortex, which then sent this information to the muscles and viscera. The muscles and viscere than react by sending information back to the cortex, and the stimulus that had simply been apprehended has now emotionally felt. 

Thus, when you run away because you see a bear and you're scared of bears, in the James's view, you don't run because you are afraid, you run first and you are afraid later, because you become aware of your body's physiological changes when you run, and then you cognitively interpret you physical reactions and conclude that what you're feeling is fright. Your emotional reaction depends on how you interpret those physical reactions. Lange went further to test this idea, due the name James-Lange theory. 

Cannon-Bard theory of emotion:

They believed that physiological responses were not distinct enough to distinguish among fear, anger, and sexual attraction, for example. They proposed that we simultaneously experience emotions and physiological reactions: the thalamus processes the emotional stimuli and sends this information simultaneously to the neocortex and to the hypothalamus, which produces peripheral response. The Cannon-Bard theory remains important because it showed that reactions to emotional stimuli could occur without the cortex, at least in nonhuman animals. 

Appraisal theory of emotion:

The Appraisal theory is a group of theories that say that emotion processing depends on an interaction between the stimulus properties and their interpretation. The theories differ about what is appraised and the criteria used for this appraisal. Lazarus proposed a version of appraisal theory in which emotions are a response to the reckoning of the ratio of harm versus benefit in a person's encounter with something. Thus, the cause of emotion is both the stimulus and its significance. Cognitive appraisal comes before emotional response or feeling, this appraisal step may be automatic and unconscious. 

Singer-Schachter theory: cognitive interpretation and arousal

Singer and Schachter agreed with James and Lange that the perception of the body's reaction was the emotion, but they also agreed with Cannon and Bard that there were too many emotions for there to be a specific and unique autonomic pattern for each. The theory proposes that emotional arousal and then reasoning are required to appraise a stimulus before the emotion can be identified. 

LeDoux's fast and slow roads to emotion:

LeDoux has proposed that humans have two emotion systems operating in parallel. One is a neural system for our emotional responses that bypasses the cortex and was hardwired by evolution to produce fast responses that increase our chances of survival and reproduction. The other system, which includes cognition, is slower and more accurate, this system generates the conscious feeling of emotion. Brain circuits that detect and respond to threats should be referred to as defensive circuits, and behaviors that occur in response to threats should be referred to as defensive behaviors. 

Evolutionary psychology approach to emotion:

They suggest that emotions can be an overarching program that directs the cognitive subprograms and their interactions. An emotion is not reducible to its effects on physiology, behavioral inclinations, cognitive appraisal, or feeling states, because it involves coordinated, evolved instructions for all of these aspects together. 

Panksepp's hierarchical-processing theory of emotion:

He hypothesized that emotions are subject to a control system with hierarchical processing. Emotion is processed in one of three ways; the most basic are the basic emotions and these arise straight from the neural networks in the subcortex. Cognition plays no further role when it comes to feeling these emotions. The core emotions arise from conditioning, and the tertiary-process emotions are elaborated by cognition. 

What is the amygdala?

The amygdala is a small, almond-shaped structure in the medial temporal lobe adjacent to the anterior portion of the hippocampus. It is a collection of 13 nuclei that can be grouped into three main amygdaloid complexes: basolateral nuclear complex, centromedial complex and the cortical nucleus. The amygdala is known for that it is the most connected structure in the forebrain in humans. It has receptors for many different neurotransmitters and for various hormones that are present in the brain. 

What is the influence of emotion on learning?

Claparède was the first to provide evidence that two types of learning, implicit and explicit, are apparently associated with two different pathways. He was a doctor who had a client with Korsakoff's syndrome. Every morning he had a ritual of shaking the hands of the clients he met. On a day he put a pin needle in his hand when he shaked hers. The next morning she, of course, didn't remember who the doctor was but as soon as he extended his hand to greet her, she hesitated for the first time. Implicit learning is a type of Pavlovian learning in which a neutral stimulus acquires aversive properties when paired with an aversive event. This is a classic example of fear conditioning. There is also a phenomenon called extinction; it represents new learning about the stimulus that inhibits expression of the original memory. 

The amygdala is necessary for implicit learning, but it is not necessary for explicit or emotional learning. The conscious knowledge of an upcoming shock (in for instance an experiment of conditioning) cannot generate physiological changes normally associated with fear if there is no link present to link it to the amygdala and its midbrain connections. Information can come to the amygdala via two separate pathways; the 'low' road - goes directly from the thalamus to the amygdala, and the 'high' road - goes from the cortex to the amygdala. 

Next to the amygdala is the hippocampus (in the state of learning) only necessary for the acquisition of a memory, but if arousal accompanies memory acquisition the strength and duration of that memory is modulated by amygdala activity. 

What are the interactions between emotion and other cognitive processes?

Much research has been focused on the effects of emotion on learning and memory, its effects on other cognitive processes are also being unraveled. 

We have a increased awareness for and pay attention to emotionally salient stimuli. Researchers often use the paradigm of the attentional blink to test this, in which stimuli are presented so quickly in succession that an individual stimulus is difficult to identify. But if participants are told to disregard all the other words, they are able to identify the targets. The proposed mechanism for this attentional change is that early in the perceptual processing of the stimulus, the amygdala receives input about its emotional significance, and, through projections to sensory cortical regions, modulates the attentional and perceptual processes. Fearful stimuli are not the only stimuli processed by the amygdala, especially fearful and disgusting ones have the priority. 

The amygdala is critical in bringing an unattended but emotional stimulus into the realm of conscious awareness by providing some feedback to the primary sensory cortices, thus affecting perceptual processing. 

A popular idea is that emotion leads people to make suboptimal and sometimes irrational decisions. The hypothesis that emotion and reason are separable in the brain and compete for control of behavior is often called 'dual-systems theory' and it has dominated Western thought since Plato. But the dualism theory has not been substantiated. Our current understanding suggests that there are two ways by which emotion influences decision making:

1. Incidental affect: current emotional state, unrelated to the decision at hand, incidentally influences the decision

2. Integral emotion: emotions elicited by the choice options are incorporated into the decision. This process may include emotions that you anticipate feeling after you have made the decision, which humans are notoriously bad at predicting.

What is the link between emotion and social stimuli?

Studies have shown that there is an dissociation between identifying an individual's face and recognizing the emotional expression on that face. Neuroimaging in normal patients and patients with anxiety disorders have reported that increased amygdala activation in response to brief representations of faces with fearful expressions are higher compared to faces with neutral expressions. The amygdala response/activation is significantly greater when in response to fear. One interesting part is that the participant does not need to be aware of the fearful face for the amygdala to respond. People who have extensive damage to the amygdala are not able to recognize fearful or untrustworthy facial expression. 

What are other important areas or emotions?

The insula is tucked between the frontal and temporal lobes in the Sylvian fissure. It has reciprocal connections with areas associated with emotion, such as the amygdala, medial prefrontal cortex, and anterior cingulate gyrus. There is a significant correlation between the insular activity and the perception of internal bodily states, known as interoception. The connections and activation profile of the insula suggest that is integrates visceral and somatic input and forms a representation of the state of the body. 

Depending on how the information is analyzed, different neuroimaging studies have been interpreted to both support and refute the theory that there are different brain areas or circuits associated with the processing of different emotions. 

How does the cognitive control of emotion work?

Emotion regulation refers to the processes that influence the types of emotions we have, when we have them, and how we express and experience them. Emotion regulation processes can intervene at multiple points during the generation of emotion, some early on and some after the fact. Researchers investigate how we regulate emotion proceed by changing the input or the output. Change to the input can consist of avoiding the stimulus altogether, or altering the emotional impact of the stimulus by reappraisal. There is also a phenomenon, suppression, where the response to a emotional stimulus is altered a certain way. It reinterprets an emotion-laden stimulus in non-emotional terms. Research shows that reappraisal can lead to reduced emotional experience, suppression on the other hand caused participants to be more aroused. 

What is the anatomy behind cognitive control?

Cognitive control, sometimes referred to as executive functions, refers to the set of psychological processes that enable us to use our perceptions, knowledge and goals to bias the selection of action and thoughts from a multitude of possibilities. The behaviors thus enables can be described as goal-oriented behavior. Cognitive control requires the integrated function of many different parts of the brain. The remainder of the frontal lobe is called the prefrontal cortex (PFC), we will refer to four regions of the PFC: lateral prefrontal cortex (LPFC), frontal pole (FP), orbitofrontal cortex (OFC) and the medial frontal cortex (MFC). In this chapter we concentrate on two prefrontal control systems. The first system, which includes the LPFC, OFC and FP, supports goal-oriented behavior. The second control system, which includes the MFC, plays an essential role in guiding and monitoring behavior. 

When compared to other primate species, the expansion of the prefrontal cortex in the human brain is more pronounced in the white matter than in the gray matter. 

What are cognitive control deficits?

From a superficial look it is very difficult to detect a neurological disorder by someone. With more specific and sensitive tests, it becomes clear that frontal lesions can disrupt different aspects of normal cognition and memory, producing an array of problems. Such patients may persist in a response even after being told that it is incorrect - this behavior is called perseveration. Ironically, patients with frontal lobe lesions are aware of their deteriorating social situation, have the intellectual capabilities to generate ideas that may alleviate their problems, and may be able to tell you the pros and cons of each idea. With a PFC lesion, monkeys demonstrate a loss of goal-oriented behavior and the behavior becomes stimulus-driven. They also have a utilization behavior, humans have prototypical responses for guiding behavior. Deficits in cognitive control are also considered a hallmark of many psychiatric conditions, including depression, schizophrenia, OCD and ADHD. A hallmark of drug or alcohol addiction is the sense of a loss of control, the disruption of PFC function may underlie the characteristic problems addicts have in inhibiting destructive behavior. 

What is goal-oriented behavior?

Researchers distinguish between two fundamental types of action. Goal-oriented actions are based on the assessment of an expected reward or value and the knowledge that there is a causal link between the action and the reward. In contrast to goal-oriented actions stand habitual actions. A habit is defined as an action that is no longer under control of a reward, but is stimulus driven; we can consider it automatic. 

The PFC appears to be an important interface between the current perceptual information and stored knowledge, and thus constitutes a major component of the working memory system. Its importance in working memory was first demonstrated in studies where animals with prefrontal lesions performed a variety of delayed-response tasks. A working memory system requires a mechanism to access stored information and keep that information active. The prefrontal cortex can perform both operations. PFC cells could simply be providing a generic signal that supports representations in other cortical areas. Research shows that in terms of stimulus attributes, cells in the LPFC exhibit task-specific selectivity. We can conceptualize working memory as the interaction between a prefrontal representation of the task goal and other parts of the brain that contain perceptual and long-term knowledge relevant to that goal.

How does decision making works?

The theories about our decision-making processes are either normative or descriptive. Normative decision theories define how people ought to make decisions that yield the optimal choice. Very often, such theories fail to predict what people actually choose. Descriptive decision theories attempt to describe what people actually do, not what they should do. We reach decisions in many different ways. The distinction is that goal-oriented decisions are based on the assessment of expected rewards, whereas habits, are actions taken that are no longer under the control of the reward. A somewhat similar way of classifying decisions is to divide them into action-outcome decisions - where the decisions involves some from of evaluation of the expected outcomes, or stimulus-response decisions - if the outcome is consistent, it becomes a stimulus-response decision. 

Decision making is about making choices that will maximize value. It is not, however, enough to think only about the possible reward level. We also have to consider the likelihood of receiving the reward, as well as the costs required to obtain that reward. 

Some rewards, such as food, water and sex are primary reinforcers: they have a direct benefit for survival fitness. The secondary reinforcers such as money and status, are rewards that have no intrinsic value themselves, but become rewarding through their association with other forms of reinforcement. Value is represented in the brain of monkeys in the ACC, anterior cingulate cortex, the LPFC and the OFC. The subjective value of an item is made up of multiple variables that include payoff amount, context, probability, effort-cost, temporal discounting, novelty and preference. The classic finding in behavioral economics, temporal discounting, is the observation that the value of a reward is reduced when we have to wait to receive that reward. Overall, the neurophysiological and neuroimaging studies indicate that the OFC plays a key role in the representation of value. 

Rewards are fundamental to the behavior of all animals. Much of the work on reward has focused on the neurotransmitter dopamine (DA). Dopaminergic cells are scattered throughout the midbrain, sending axonal projections to many cortical and subcortical areas. Schultz proposed a new hypothesis to account for the role of dopamine in reward-based learning. Rather than thinking of the spike in DA neuron activity as representing the reward, he suggested that it should be viewed as a reward prediction error (RPE), a signal represents the difference between the obtained reward and the expected reward. The RPE is used as a learning signal to update value information as expectancies and the valence of rewards change. The activity of some DA neurons provides a neuronal code of prediction errors. 

How does goal planning work; how do you stay on a task?

Once humans choose a goal, we have to figure out how to accomplish it. Three components are essential for successfully developing and executing an action plan:

1. The goal must be identified and subgoals developed

2. In choosing among goals and subgoals, consequences must be anticipated

3. Requirements for achieving the subgoals must be determined

When an action plan is viewed as a hierarchical representation, it is easy to see that failure to achieve a goal can happen in many ways. The different activation patterns show that different subregions of the PFC are required for things like response selection or rule specification. A key idea of hierarchy, however, is that processing deficits will be asymmetrical. Individuals who fail at operations required for performance at the lower levels of a hierarchy, will also fail when given more challenging tasks. Making wise decisions with complex matters, such as long-term financial goals, requires keeping an eye on the overall picture. Therefor we must evaluate the different subgoals. 

Goal-oriented behavior requires selecting task-relevant information and filtering out task-irrelevant information. Selection refers to the ability to focus attention on perceptual features or information in memory. The PFC has been conceptualized as the dynamic filtering mechanism through which the task-relevant information is activated and maintained in working memory. Cognitive control is also essential when we need to maintain multiple goals at the same time. This is especially needed when those goals are unrelated. With practice, the brain develops connectivity patterns that enable people to efficiently shift between different goals. The prefrontal cortex helps make action selection more efficient. This benefit of using experiences to guide action selection may also come at a cost in terms of considering novel ways to act, given a specific situation. 

What are the mechanisms of goal-based selection?

Dynamic filtering of the PFC can influence the contents of information processing in at least to distinct ways. One is to accentuate the attended information. When multiple sources of information may come from the same location, we might selectively enhance the task-relevant information or inhibit the irrelevant information. Evidence for a loss of inhibitory control with frontal lobe dysfunction comes from electrophysiological studies. All people will have experienced similar situations, whereas you put your keys down somewhere, but you forgot where you put them. Goal-oriented behavior involves the amplification of task-relevant information and the inhibition of task-irrelevant information. 

Patients who have lesions in the prefrontal region have difficulty with and loose their inhibitory control, for instance, they are unable to inhibit task-irrelevant information. That's why they are not good at keeping their eyes on one goal, and take in a lot of noise. The inhibition of action on the other hand constitutes of another form of cognitive control. The right inferior frontal gyrus and the subthalamic nucleus are important for this form of control. 

How can you ensure that goal-oriented behaviors succeed?

Researchers proposed a psychological model of cognitive control, outlining the conditions under which the selection of an action might require the operation of a high-level control system, or what they referred to as a supervisory attentional system (SAS). These include the following situations:

• Planning or decision making is required

• Responses are novel or not well learned

• The required response competes with a strong, habitual response

• Error correction or troubleshooting is required

• The situation is difficult or dangerous

One might expect the task of a monitoring system to be like that of a supervisor, keeping an eye on the overall flow of activity, ready to step in whenever a problem arises. The last 30 years have witnessed burgeoning interest in the medial frontal cortex (MFC) and in particular the anterior cingulate cortex (ACC) as a critical component of a monitoring system. Damage to the ACC was associated with akinetic mutism, a disorder characterized by minimal movement including the absense of speech. The medial frontal cortex becomes engaged whenever a task becomes more difficult - the type of situations where monitoring demands are likely to be high. 

Attentional hierarchy hypothesis

An early hypothesis centered on the idea that the medial frontal cortex should be conceptualized as part of an attentional hierarchy. The MFC occupies an upper rung on the hierarchy, playing a critical role in coordinating activity across attention systems. 

Error detection hypothesis

When people make an incorrect response, a large evoked response sweeps over the prefrontal cortex just after the movement is initiated. This signal, referred to as the error-related negativity (ERN) when time-locked to the response, and the feedback-related negativity (FRN) when time-locked to feedback, has been localized to the anterior cingulate. We make errors when we are not paying much attention to the task at hand. This response is all generated by the medial frontal cortex. 

Response conflict hypothesis

A key function of the medial frontal cortex is to evaluate response conflict. This hypothesis is intended to provide an umbrella account of the monitoring role of this region, encompassing earlier models that focused on attentional hierarchies or error detection. The medial frontal cortex is also engaged when the response conflict is high. Through its interactions with lateral regions of the prefrontal cortex, a monitoring system can regulate the level of cognitive control. 

What is the mind-brain problem?

The problem of consciousness, or otherwise known as the mind-brain problem was originally the realm of philosophy. Dualism, from Descartes, states that the mind and brain are two distinct and separate phenomena, and that conscious experience is nonphysical and beyond the scope of the physical sciences. Materialism asserts that both mind and body are physical mediums and that understanding the physical workings of the body and brain well enough will lead to an understanding of the mind. 

The definition of consciousness is: consciousness is having perceptions, thoughts, and feelings; awareness. The conscious state has a lot of possible contents. But, explaining how the firing of neurons generates sentience is known in the world as the 'hard problem' of consciousness and some people think it will never be explained. The hard problem holds explaining how the chemical interactions of the body produce our subjective conscious experience. 

What is the anatomy of consciousness?

The processes that are apparent in the brainstem and thalamus are sufficient for an organism to be alive, awake, alert and aware of the current moment and place someone or something is currently in. The reticular activating system is involved in arousal, regulating the sleep-wake cycle and mediating the attention. Our conscious experience is expanded by processing in the cerebral cortex.

What are the levels of arousal and consciousness?

While a level of wakefulness is necessary for consciousness, consciousness is not necessary for wakefulness. Patients with unresponsive wakefulness syndrome, or the vegetative state, are 'awaken' from a coma. They are not conscious, in contrast with a minimally conscious state patient, who can localize pain and nonreflex movements. Complicating the diagnosis is the locked-in syndrome, a condition in which one is unable to move any muscles but is fully conscious and has a normal sleep-wake cycle. LIS is caused by a lesion to the ventral part of the pons in the brainstem, where neurons connect the cerebellum with the cortex. 

The sleep-wake cycle is regulated by a complex interplay of neurotransmitters, neuropeptides, and hormones released by structures located in the basal forebrain, hypothalamus and brainstem. The overarching controller is the biological clock, suprachiasmatic nucleus (SCN) in the hypothalamus. It receives light input directly from the retina, allowing its neurons to synchronize to the day-night cycle. 

When we fall asleep the brain passes through distinct brain states with typical patterns of EEG activity. Stage 4 non-rapid eye movement (NREM) sleep, is where our brain waves are less frequent and have a higher amplitude. Then, throughout the night, we cycle between rapid eye movement (REM) sleep, which has low-amplitude more frequent brain waves. It is also investigated that during sleepwalking, the brain areas that mediate the cognitive control and emotional regulation are asleep. 

What is the organizational architecture of complex systems?

The vast majority of mental processes happen outside of our conscious awareness. The brain is a complex system, and understanding the organization of the parts is also necessary in order to relate the system's structure to its function. The complex system of your brain is a system of systems. A layer can be a single module or groups of modules. Each layer acts independently because if has its own specific protocol, rules that stipulate the allowed interactions, both within a layer and between adjacent layers. 

Understanding that protocol doesn't dictate an outcome is important. The idea that there are many ways to implement a system to produce one behavior is known as multiple realizability. Knowing how it works on a certain level in the organization of the brain, does not automatically mean that you can also predict how the actual functioning is at another level. 

How do you have access to information?

Blindsight refers to the phenomenon in which some patients suffering a lesion in their visual cortex can respond to visual stimuli presented in the blind part of their visual field. But these activities happen outside the realm of the consciousness of the patient. 

Next to blindsight there are a lot of processes active in the brain that go by nonconsious. We only have conscious access to a limited amount of information that is processed by the brain. The subliminal processing of activity in the brain is defined as brain activity that is evoked by a stimulus that is below a certain threshold for awareness. When processing is subliminal, the information is inaccessible to awareness. 

We humans also have the ability to relegate learned tasks and also memories to be put into the nonconscious processing. This enables us to devote our limited time and consciousness attention to the resources that are important, so we can recognize and adapt to certain changes and novel situation in the environment, thus increasing your own change of survival. 

Can mental states affect brain processing?

Any theories about consciousness must consider the question of whether a conscious thought has any control over the brain that processes it. The brain is a decision-making device, guided by experience, that gathers and computes information in real time to inform its decisions. The idea is, and research has shown, that people who believe in having a free will behave differently from those who do not believe in a free will, suggesting that a mental state can affect behavior. 

What are the contents of animal consciousness?

Researchers have looked for evidence or consciousness by studying animal behavior such as tool use and conducting mirror self-recognition tests. Evidence has recently been found that chimpanzees understand that others' behavior is guided by beliefs. Different species of animals also have different contents to their conscious experience, depending on the neural processing that they possess, which in turn is a product of evolution. 

What is sentience?

Sentience encompasses the subjective qualia, phenomenal awareness, raw feelings, and first-person viewpoint of an experience - what it is like to be or do something. 

If the universe and everything in it follow a set of determined laws, then, it was inferred, everything must be determined, including people's behavior and, in fact, their entire lives. Determinism is the philosophical belief that all current and future events and actions, including human cognition, decisions, and behavior are caused by preceding events combined with the laws of nature. 

The quantum theory was developed to explain not just black-body radiation, but also the emission of electrons from the surface of a metal in response to light, as well as why, when an electron loses energy, it stays in orbit and doesn't crash into the nucleus.