Cognitive Neuroscience, the biology of the mind, by M. Gazzaniga (fourth edition) – Summary chapter 9

Learning refers to whenever experience or interaction with the environment results in changes in behaviour. Memory refers to the complete collection of experiences that have been stored in the brain. Learning occurs in three steps: encoding (1), consolidation (2), retrieval (3).

Iconic memory is the memory storage for visual information. It can store information for ±500ms and can be assessed using Sperling’s whole-report/partial-report task. People’s performance is better for partial-report. Echoic memory is the memory storage for auditory information. It can store information for ±10s. A deviant tone evokes a ‘mismatch negativity’ when there is little time between the tones. In both types of memory, there is a passive decay of information.

The modal model states that information is first stored in sensory memory, then it can move, using attentional processes, to short-term storage. If the item is rehearsed, it can be moved into long-term memory. At each stage, memory can be lost by decay, interference or a combination of the two.

The working memory is the interface of memory. It is used to manipulate information, focus attention and operates over a few seconds. The storage of working memory is ±3/4 items and can be assessed using the change detection paradigm. It contains three parts:

1. Visuospatial sketchpad
   Information storage in visual- or visuospatial codes. It consists of a bi-hemispherical network containing the parieto-occipital region and is more strongly located in the right hemisphere.
2. Central executive
   Command and control centre that coordinates actions between two subordinate systems.
3. Phonological loop
   Information coding in acoustical codes. It consists of a left-hemisphere network containing the lateral frontal and inferior parietal lobes.

Long-term memory consists of declarative memory (explicit memory), memory of events and facts and non-declarative memory (implicit memory), memory of skills. Episodic memory refers to memory about life-events. Semantic memory refers to memory of facts.

The hippocampus is important for encoding and retrieval of information. The function of the hippocampus may be to bind contextual information together to form a complex contextual memory. The perirhinal cortex supports recognition based on familiarity. The left frontal cortex is involved in encoding episodic information and the right frontal cortex is involved in the retrieval of episodic information. Retrieval of information from long-term memory reactivates brain areas active during encoding.

The working memory maintenance hypothesis states that activation of the parietal cortex is related to the maintenance of information in working memory. The binding of items and context model states that the perirhinal cortex represents information about specific items, the para-hippocampal cortex represents information about the context and processing in the hippocampus binds the representation of items with their context. Every time something is retrieved from memory, there is a new memory trace in the hippocampus. The more often something is retrieved, the more memory traces there are in the hippocampus. 

Priming effects occur because the processing of a stimulus for a second time is better and faster. There are three forms of priming: perceptual priming (1), conceptual priming (2) and semantic priming (3). Perceptual priming happens in the sensory cortex and becomes weaker the less the stimulus resembles the priming stimulus.

If a stimulus is repeated over and over again, there will be less neural activity. The sharpening theory states that only the relevant neurons will become active after repeated exposure.

Procedural memory is the memory for skills. Learning of skills consists of two phases. In the early learning phase of skills, the basal ganglia, cerebellum, posterior parietal lobe and premotor cortex are used. In the late learning phase of skills, there is less activity in these areas and a shift from associative areas to motor regions in basal ganglia and cerebellum. Complex abilities require fast and accurate integration of motor-, perceptual- and cognitive skills. Neural activity of motor skills can be measured using the serial reaction task (SRT). Participants in the serial reaction task speed up when there is a sequence, even without awareness of the pattern.
Conditioning makes use of the cerebellum and makes use of the amygdala if conditioning consists of an emotional component.

On a cellular basis, memory can be linked to changes in neural connectivity and the strength of synaptic transmission. Hebb’s law states that ‘what fires together, wires together’. Memory makes use of long-term potentiation (LTP), a long-lasting increase in communication between neurons and long-term depression (LTD), long-lasting decrease in communication between neurons.

LTP can occur after one burst (1), can last for weeks (2), is very specific (3) and is associative (4). Possible structural changes after LTP are more presynaptic vesicles (1), more postsynaptic receptors (2), more synaptic zones (3) and more synapses (4). 

LTP depends on NMDA-receptors. The NMDA-receptor’s ion channel is blocked by a magnesium ion. If glutamate binds to the NMDA-receptor and the cell membrane depolarizes, the magnesium ion is expelled and then there is an influx of calcium. NMDA-receptors are necessary to initiate LTP, but not to maintain it.

Anterograde amnesia is loss of memory for events and knowledge after a lesion. Retrograde amnesia is loss of memory for events and knowledge before a lesion. Ribot’s law states that recent memories are more likely to be lost than remote memories. Amnesia is the most severe if the hippocampus and surrounding regions are damaged.