How do we achieve goals and meet needs? - Chapter 12

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.