Cognitive Neuroscience COGNITIVE NEUROSCIENCE By YAN Zhixiong Ph

Cognitive Neuroscience COGNITIVE NEUROSCIENCE By YAN Zhixiong Ph. D

Cognitive Neuroscience EXECUTIVE FUNCTION AND HIGHER-ORDER THINKING

THEORETICAL PERSPECTIVES • Some theorists have discussed executive function in almost philosophical terms, speaking of the frontal lobes as playing an important role in a person’s ability to exert his or her will. • Others have conceptualized the frontal lobe as a controller that aids in the selection of choices to produce a particular behavior. • Regardless of how the issue is framed, the guidance or control of behavior toward a goal is probably a signature aspect of executive function, and it is equally clear that the frontal lobe plays a prominent role.

CONTROLLED VERSUS AUTOMATIC PROCESSES • Implications for patients with frontal lobe damage: • Few deficits are observed in fairly routine situations in which the appropriate response is evoked by a stimulus in a simple and obvious way. • They will appear disinhibited, with an inability to control behavior or urges, including those in the social realm. • Their behavior can sometimes be triggered by stimuli in the environment, referred to as environmental dependency syndrome. • A main seeing a hammer and nail hangs a painting in someone else’s house • A woman starts to dry dishes unasked in someone else’s home. . • They often exhibit perseveration, which is the behaviour of repeating the same action (or thought) over and over again.

CONTROLLED VERSUS AUTOMATIC PROCESSES • Like Shallice’s theory, theory of Stuss and Benson (1986) suggests that the frontal lobes are especially important in regulating behavior in nonroutine situations or in situations in which behavior must be carefully constrained. • Their model links the degree of control to particular neural substrates in a hierarchical manner. • At the lowest level, sensory information and simple tasks are processed by posterior regions of the brain in a relatively automatic manner that varies little from day to day. • The next level of control is associated with the executive, or supervisory, functions of the frontal lobe. • The highest level of control involves self-reflection and metacognition. • Self-reflection allows an individual to have self-awareness and to understand the relationship of the self to the environment; metacognition is the ability to reflect upon a cognitive process.

GOAL-DIRECTED BEHAVIORS • Guiding behavior toward a goal is not a simple function, but rather is multifaceted. • The loss of any facet of goal-oriented behavior can cause the entire plan to be derailed. • Completing a task involves a number of skills: staying on task; sequencing, or planning, information; modifying strategies; using knowledge in your plans; and monitoring actions.

INITIATION OF BEHAVIOR • One difficulty often observed in patients with executive dysfunction is referred to as psychological inertia. • Patients with executive dysfunction are poor at starting an action or a behavior, but once engaged in it, they have great difficulty stopping it. • Patients with damage to medial frontal regions, including the supplementary motor area and anterior cingulate, show differential difficulty in responding quickly compared to patients with damage in other frontal regions. • Growing evidence also implicates regions of the medial prefrontal cortex as being involved in determining how much “effort” will be exerted to reach a goal. Increased activation is observed in dorsal regions of the anterior cingulate cortex and the pre-SMA, as more physical effort is expended to get a reward.

CREATION AND MAINTENANCE OF A GOAL OR TASK SET • One of the most basic prerequisites for meeting a goal is the ability to stay on task. Patients with frontal lobe damage are notorious for “wandering off task. ” • Patients with damage to lateral prefrontal regions of the left hemisphere have difficult in task setting. • Neuroimaging studies also show increased lateral prefrontal activity when a task set is difficult to maintain, such as on the Stroop task requiring one to name the ink color in the face of competing information (RED vs. RED). The greater the difference in the nature of the task set from the prior trial, the greater the activity in these regions. • Activation is observed in lateral prefrontal regions when a cue indicates which task needs to be performed

CREATION AND MAINTENANCE OF A GOAL OR TASK SET • If more than one task set needs to be maintained, frontopolar cortex (BA 10) is likely to play a role • This area likely integrates processing for two or more separate operations for a higher goal. • For example, it may help to process subgoals and then integrate information to determine if goals are being met. • This issue can also be investigated by comparing brain activity when people choose which task to perform compared to when they are told what task to perform. • More activity is observed in dorsolateral prefrontal cortex (DLPFC) and in portions of the anterior cingulate cortex • Other studies have reported activity in frontopolar regions as well consistent with the idea that this region is involved in selecting which of the potential task sets is to be employed.

SEQUENCING AND PLANNING • The sequencing of behavior requires knowing what comes before and what comes after. • Neurons in prefrontal cortex can distinguish between those tasks that have just been accomplished versus those tasks that are about to be performed. • Individuals with frontal lobe damage have difficulty remembering the sequence in which items appears • This difficulty is observed regardless of whether they are passively watching the sequence of events or if they control the order of events. • However, they have no difficulties in item memory, as they are able to distinguish items that appeared in the sequence vs. those that did not.

SEQUENCING AND PLANNING • One task that reveals deficits in sequencing in patients with frontal lobe damage is the self-ordered pointing task, • Individuals are shown an array of items, anywhere from six to twelve, all of which are from the same category (e. g. , abstract designs or high-imagery words). • Individuals must point to a unique item on each trial • Deficits on this task are observed after frontal lobe damage, most notably lateral damage. • These regions are also active in neurologically-intact individuals when they must make a recency judgement.

SEQUENCING AND PLANNING • Another important aspect of sequencing behavior is the ability to choose which sequence or strategy best allows a goal to be attained. • Patients with frontal lobe damage are less likely to report that they use strategies, • When they do use a strategy, it tends to be ill-defined or invoked inconsistently • One task used to measure strategy and sequencing is the Tower of London • Dorsolateral prefrontal activity is observed to an increasing degree with increased difficulty of the task. • Performance on this task can be altered by t. DCS over lateral prefrontal regions

SHIFTING SET AND MODIFYING STRATEGIES • The classic neuropsychological test used to examine task-switching is the Wisconsin Card Sorting Test (WCST). • Participants are not told on what dimension (color, number, shape) cards should be sorted, but only whethere response is correct or not. • After the participant correctly sorts 10 cards on the basis of one particular attribute (e. g. , color), the criterion for sorting the cards is changed (e. g. , to shape). • Neurologically intact people quickly realize that their behavior previously no longer leads to a correct response. Hence, they adjust their responses accordingly. • In contrast, people with executive dysfunction perseverate, which is the action of continuing to engage in the same behavior.

SHIFTING SET AND MODIFYING STRATEGIES • A variety of brain areas are activated during performance of the WCST including: • DLPFC, ventrolateral prefrontal cortex the inferior parietal lobe, temporoparietal association cortex, and the basal ganglia. • This diversity of brain regions indicates that the WCST is a complex task. • One of the main components of the WCST is task- or set-switching. • Research with neurologically intact people shows there is a cost to switching between tasks • On some trials, repeat trials, the person performs the same task as on the prior trial. • On other trials, switch trials, the person performs a different task than on the prior trial. • Response times are longer for switch trials than for repeat trials, known as the switch cost. • This cost is difficult if not impossible to eliminate. • This increase in response-time reflects two factors: • a need to inhibit or overcome the prior task set, sometimes referred to as task-set inertia, and • the need to configure the system for the current task set. • Task-switching is likely to be directed by an executive control system that is independent of the systems that actually perform each of the individual task.

SHIFTING SET AND MODIFYING STRATEGIES • Patients with left frontal lobe damage have a specific deficit in task-switching, • especially when there are no obvious cues as to which task should be performed when. • Their difficulty occurs regardless of whether the switch involves a conceptual set or a perceptual set. • Conversely, increasing activity over the (left) dorsolateral prefrontal cortex via transcranial direct current stimulation can augment task-switching abilities. • Meta-analyses of brain imaging studies also implicate lateral prefrontal regions in task-switching, more specifically the inferior frontal junction.

SHIFTING SET AND MODIFYING STRATEGIES • A number of neuroimaging studies suggest it is not just a single brain region that flips the switch from Task A to Task B. • Rather task-switching involves the coordination of activity over frontal regions (including the inferior frontal junction) and parietal lobe regions, regardless of the particular tasks being performed. • In addition to activation of these fronto-parietal regions involved in task-switching generally, activation is also observed in additional brain regions. • These regions vary depending on: • the type of switch (e. g. , based on perceptual or abstract information) • the degree of similarity or dissimilarity between the task sets

SELF-MONITORING AND EVALUATION • Not surprisingly, the ability to evaluate one’s own behaviour is affected by frontal lobe lesions. • First, metacognitive awareness, that is, an overall evaluation of one’s performance, is disrupted in patients with left or right frontal lesions. • On questionnaires about their behavior, such patients are likely to say that they are organized or don’t drift off task, when those close to them, such as family members and caregivers, disagree. • This deficit does not arise from brain damage in general, as patients with lesions to left or right posterior regions are significantly more realistic in their self-assessment. • In addition, frontal damage, especially right frontal damage, impairs the ability to detect errors and to modify ongoing behaviors to take a corrective action.

SELF-MONITORING AND EVALUATION • We have a particular set of brain mechanisms that helps to monitor our performance and detect errors. • Evidence for one such mechanism comes from an ERP signal known as the error-related negativity (ERN). • It occurs approximately 100 ms after an error has been made • its amplitude increases under conditions in which response accuracy is emphasized versus speed • the larger the error (pushing the button with the wrong hand as well as the wrong finger), the larger the amplitude of the ERN. • A variety of converging evidence suggests that the ERN component arises from rostral regions of the anterior cingulate

SELF-MONITORING AND EVALUATION • One initial suggestion was that the anterior cingulate actually detects that an error has been made. • But other evidence suggests that even when a person is not aware of an error, an ERN can be still be detected. • Hence, it may be that the ERN is just providing a rather undifferentiated signal that something is amiss. • Instead, awareness of an error is indexed by another component, the error positivity (Pe), which frequently follows the ERN by about 200– 300 ms. • The source of this component remains unclear, but it may be generated in the insula, a brain region associated with interoception, the ability to sense the physiological condition of the body • Localization of the error positivity to this region of the brain seems reasonable, as we often have that “Oops” feeling in the pit of our stomach, when we realize that we’ve make a big mistake.

INHIBITION • The inability to stop, interrupt, or abort inappropriate responses, often referred to response inhibition, is considered by some models to be a major subcomponent of executive function. • These abilities are compromised in patients with frontal lobe damage • Response inhibition is investigated using a number of paradigms. • In the Go/No-Go task, the person responds by pushing a button when certain visual stimuli appear (Go trials) and withholds response to other stimuli (No-Go trials). • Response inhibition is quite difficult when the No-Go trials are relatively rare, because Go responses are expected and prepotent. • In neuroimaging studies, withholding a response has consistently been found to engage a right-sided network of regions, including the right middle and inferior frontal cortex, the pre-SMA, and parietal cortex.

INHIBITION • In the Stop-signal task, the person must respond as quickly as possible to a stimulus that appears on the screen. • However, on a minority of trials, very shortly (e. g. , one-quarter of a second) after the stimulus is presented, another signal (e. g. , auditory tone) occurs. • This tone indicates that the response should be aborted. • This task differs from the Go/No-Go task • In that task the person must override the tendency to produce a prepotent response • But in the Stop-signal task, the person must actually cancel an ongoing response. • This task too activates a large network of brain regions, spanning (dorso)lateral prefrontal cortex, the anterior cingulate, SMA, pre. SMA, insula, and parietal regions.

HIGHER-ORDER THINKING • Executive function is often conceptualized to include a set of abilities known as higherorder thinking. • This term describes more complicated aspects of thought, such as • being able to think in an abstract and conceptual rather than concrete manner, • the ability to deduce rules or regularity, and • the ability to be flexible and respond to novelty.

HIGHER-ORDER THINKING: ABSTRACT AND CONCEPTUAL THINKING • One deficit exhibited by patients with executive dysfunction is an inability to process material in an abstract rather than a concrete manner. • When reading metaphorical sentences, activity is greater in many areas of prefrontal cortex compared to when reading literal sentences. • Another way to examine the issue of abstract thinking is to examine analogical reasoning.

HIGHER-ORDER THINKING: ABSTRACT AND CONCEPTUAL THINKING • Meta-analyses of neuroimaging data indicate that a variety of regions are activated during analogical reasoning, regardless of whether verbal or visuospatial problems are solved. • These include frontopolar and dorsolateral prefrontal regions, as well as the anterior insula and parietal cortex • In addition distinct areas in frontopolar cortex activate for visuospatial analogies as compared to semantic analogies, which tend to be in a verbal format. • This pattern suggests both common mechanisms for such reasoning as well as more specific regions that vary with problem type (i. e. , spatial, verbal). • Anterior temporal regions involved in semantic processing may also be important for analogical reasoning as anatomical variation in these regions is associated with an individual’s level of anaological reasoning

HIGHER-ORDER THINKING: RULES AND INFERENCE • Another form of abstract thinking is the ability to deduce or invoke a rule. • Single-cell recordings from cells in the frontal lobe of monkeys indicate there are neurons that allow for the coding of “rules. ” • Some frontal lobe patients have difficulty with abstraction and rule-like understanding • For example, whereas some people with frontal lobe damage exhibit only perseverative tendencies on the WCST, others cannot even figure out the criterion by which cards should be sorted. • In neuroimaging studies, a variety of tasks have been used to provided insights into the neural substrates of abstract rule-governed behavior in neurologically intact individuals. • Some studies compare activation in conditions in which a person is told what rule should govern his or her behavior, compared to when the person must deduce that rule. • Yet another way to examine rule-governed behavior is for people to make decisions about whether inferences are valid. Is the circled relationship valid, given the relationships above it?

HIGHER-ORDER THINKING: RESPONSE TO NOVELTY • Novelty, is an event, a situation, or an action that has a low probability of occurring given a particular context. • The ventral attentional system is proposed to allow novel stimuli to capture attention. • Electrophysiological studies also implicate frontal regions as playing an important role when a novel stimulus captures attention. Response to truly novel (checkboard) stimuli (red line) and to rare target (large blue circle) stimuli (blue line) stimuli among a set of frequent smaller blue circles (not shown) The novel stimulus elicits an earlier P 3 a over frontal regions while the rare stimulus elicits a later P 3 b over more posterior regions.

JUDGMENT AND DECISION MAKING • Almost any clinician who treats or works with people who have executive dysfunction will invariably report that the judgment and decision-making abilities of such people are compromised. • The knowledge base of these people usually remains relatively unaffected, • However, if the task becomes a bit more abstract, they begin to exhibit difficulties. • The neural underpinnings of decision making have been an especially vibrant topic of research lately. • This work tends to focus on a particular psychological phenomenon, such as how people evaluate risk versus reward or how much time people are willing to wait for a reward. • The frontopolar cortex has been implicated as being particularly important for abandoning the current strategy and trying a new one, consistent with its role in processing novelty. • Relatedly, frontopolar cortex appears to be able to hold information about “The road not taken” in reference to the current course of action.

JUDGMENT AND DECISION MAKING • Another paradigm often used to examine decision making is the delay discounting paradigm, also sometimes referred to as an intertemporal choice task • In this paradigm, an individual must decide whether they would like a smaller reward now ($5) or a larger reward in the future ($10 in a week). • Some researchers argue that the value of both present and future rewards are calculated by medial orbitofrontal regions • Other research suggests that dorsolateral prefrontal regions are engaged when an individual must overcome the temptation to take the immediate monetary reward or to choose atasty piece of cake rather than the healthy but less mouth-watering carrot. • This idea is supported by findings that TMS over left dorsolateral prefrontal cortex bias people towards taking the immediate reward

ORGANIZATION OF THE BRAIN FOR EXECUTIVE FUNCTION • The organization of the frontal lobe for executive function is quite complicated. • There is unlikely to be a strict subregion-to-function mapping. • Rather, overlapping regions are involved in most of the functions we have described. • Nonetheless, researchers have attempted to derive some principles or general trends concerning how prefrontal cortex might be organized for executive function.

ORGANIZATION OF THE BRAIN FOR EXECUTIVE FUNCTION • One model argues that there is a nested hierarchy of control from caudal to rostral portions of frontal cortex • The most posterior regions being influenced by the most immediate aspects of a situation and more anterior regions affected by the larger context. • This nested-hierarchy model focuses on the type of information that is used to guide control. Sensory control: Your phone rings, you read your text message Contextual control: Your phone rings in class, you do not read your text message Episodic control: On this particular occasion, since you are waiting to hear about the outcome of your parent’s surgery, ven though you are in class, when your phone rings, you read your text message Branching control: I fyou really want to show the person with whom you are speaking that you care about her/him, you do not read your text message when your phone rings. But both of you are lost and trying to get to a restaurant where you are meeting friends, when your phone rings, you read your text message as it may contain information on how to get to the restaurant.

ORGANIZATION OF THE BRAIN FOR EXECUTIVE FUNCTION • Another posits a hierarchy based on the nature of representations that are competing for control over action selection. • More posterior regions may select actions on the basis of more concrete response dimensions (e. g. , pick the flowers nearest my hand) or simple decision trees (If the flowers are for my partner, get tulips; if they are for my mom, get daisies) • More anterior regions may select actions on the basis of more abstract dimensions, such as the context (if it is Valentine’s Day, buy crimson roses) or based on decision trees with more levels • If it is not Valentine’s Day then: If the flowers are for my partner, get tulips; if they are for my mom, get daisies, • but If it is Valentine’s Day then: If the flowers are for my partner get red roses; if they are for my mom, get white roses

ORGANIZATION OF THE BRAIN FOR EXECUTIVE FUNCTION • Other models focus on the relationship between lateral and medial regions. • One viewpoint is that selection or control processes involve prefrontal regions that exert control at different times, • from task preparation to stimulus processing to response output and then response evaluation. • This model views control as implemented in a temporal cascade involving lateral and medial prefrontal regions

A CENTRAL ROLE FOR WORKING MEMORY IN EXECUTIVE FUNCTION • Researchers have argued that DLPFC may play a central role in executive function because it supports working memory. • This is not to say that executive function is synonymous with working memory • Rather, as outlined in psychological theories, working memory plays a central, prominent role in executive function. • If one cannot maintain information in working memory, one may not be able to keep a goal in mind • Such a deficit would interfere with a person’s ability to direct behavior toward a goal or to formulate a strategy for attaining the goal. • In addition, difficulty in keeping information on-line may disrupt a person’s understanding of temporal relations between items and events. • If what has just happened cannot be kept on-line, its relation to subsequent happenings will be lost. In such cases, sequencing would be quite difficult. • Moreover, if one is not able to retain multiple pieces of information simultaneously in working memory, there will be difficulty in creating or following rules, in making inferences, and/or in understanding the relations between items in the world.