PJ

Executive Functions

  • Executive Functions
    • Involve impairments in forming, updating, and implementing rules for effective behavior.
    • Act on rules for behavior, unlike attentional functions that modulate sensory information.
    • A metaphor is a switch operator controlling tracks in a railroad yard, setting up new track patterns to maximize efficiency and success.
    • Executive processes set up rules for information flow in other brain regions to meet demands and achieve goals.
    • Initiating Rules for Behavior
    • Damage to the lateral prefrontal cortex impairs the ability to initiate motor movements, complex actions, and mental plans.
    • Patients with lateral prefrontal damage show little spontaneity, withdraw from society, and show little concern about their abnormal personality.
    • Abulia: Motor deficits characterized by lethargy, quiet withdrawal, slow movement, and distractibility due to strokes or lesions in lateral frontal lobes.
    • Prefrontal cortex neurons carry information about rules in a distributed manner, with populations of neurons coding for different rules depending on context.
    • Creating new rules involves the basal ganglia, which are important for mapping a specific stimulus to a specific response, as shown in category learning tasks using fMRI and lesion studies.
    • Parietal cortex contributes to rule creation, encoding the expected value of possible actions and maintaining the set of possible actions.
    • Inhibiting Rules for Behavior
    • It involves suppressing unimportant information, halting behaviors, preventing irrelevant information, and restraining inappropriate actions.
    • Lateral prefrontal cortex implicated in inhibition processes through ERPs and fMRI.
    • Oddball task: Target stimuli evoke the P300 ERP component and activate dorsolateral prefrontal cortex.
    • Go/no-go task: No-go stimuli activate lateral prefrontal and parietal cortices; deficits seen in schizophrenia.
    • Stop-signal task: Damage to posterior ventrolateral frontal cortex impairs response inhibition; deficits seen in ADHD and Parkinson’s disease.
    • Inhibitory processes prevent task-irrelevant information from interfering with performance.
    • Prefrontal patients show increased amplitude of early-latency ERP components in sensory cortices, impairing the ability to keep task-relevant information online.
    • Distraction impairs performance on delayed match-to-sample tasks in prefrontal patients.
    • Inhibiting Socially Inappropriate Behaviors
    • Ventral prefrontal cortex damage causes a failure to match behavior to social rules, leading to argumentativeness and aggression.
    • Acquired sociopathy: Blunted emotional affect, poor decisions, and difficulty interacting with others due to trauma or disease.
    • Congenital sociopathy: Difficulty expressing reasoning behind social rules, goal-directed behavior, and lack of remorse.
    • Ventromedial prefrontal damage impairs social behavior but not necessarily the cognitive appreciation of rules.
    • Patients with ventromedial prefrontal cortex damage in infancy show habitual misbehavior and an inability to comprehend social rules.
    • Shifting Among Rules for Behavior
    • Goal-directed behavior requires shifting among different rules as goals change.
    • Wisconsin Card Sorting Test: Patients with prefrontal damage continue to use previously valid rules despite negative feedback, known as perseveration.
    • Adaptive performance on the test is correlated with measures of inhibition.
    • Ventral frontal lobes, especially the orbitofrontal cortex, facilitate shifting between rules in situations involving reward and punishment.
    • Damage to the orbitofrontal cortex impairs learning the relationship of stimuli and rewards, as seen in reversal learning tasks.
    • Lateral prefrontal damage can also lead to deficits in reversal learning.
    • Inability to recognize a context change leads to inappropriate persistence of a previously relevant behavior.
    • Relating Rules to Create Higher-Order Models of the World
    • Inability to create abstract representations, a core feature of frontal lobe damage.
    • Patients with prefrontal lesions are unable to integrate pictures into a coherent narrative and give literal interpretations of proverbs.
    • Intelligence testing has a long history, with the IQ test developed by Alfred Binet being the best-known example.
    • Intelligence comprises separate components such as verbal and mathematical abilities.
    • Humans and great apes have large frontal lobes, suggesting that the frontal lobes are important in mediating intelligence.
    • Variations in how the brain matures predict differences in intelligence across individuals.
    • Patients with damage to frontopolar cortex exhibit reduced performance when solving complex patterns.
    • Frontopolar activation is observed when abstract information from different sources must be integrated to form a more general rule.
    • Simulation deficits are evident in tasks requiring planning or processing the future consequences of actions, such as the Tower of London puzzle.
    • Frontopolar cortex is critical for implementing higher-order goals, balancing reward-seeking (exploitative) and information-seeking (exploratory) goals.
    • Hierarchical Models for Executive Function
    • Posterior regions are related to motor behavior, while anterior regions support reasoning and mental simulation.
    • Rostral-caudal organization of the frontal lobes according to increasing abstraction of executive functions.
    • Temporal abstraction: Executive functions are organized according to their level of temporal abstraction, with posterior regions supporting simple functions and anterior regions supporting long-term goals.
    • Policy abstraction: More anterior regions support higher-order policies for behavior, needed to determine which of several simple rules applies in the current context.
    • Control: Matching Behavior to Context
    • Executive functions carry a cost and must be implemented effectively.
    • Behavioral actions must be monitored and conflicts between actions must be resolved.
    • Conflict Monitoring
    • Depends on the anterior cingulate gyrus in the midline frontal lobe.
    • Anterior cingulate cortex activation increases under conditions of high conflict between responses, such as in the Stroop task.
    • Increased activation in the anterior cingulate cortex results in increased activation in the dorsolateral prefrontal cortex.
    • Executive processes evoke activation in the dorsal part of the anterior cingulate gyrus, whereas affective processes evoke activation in more anterior and ventral parts.
    • The error-related negativity (ERN) follows mistaken actions and correlates with response time on the subsequent trial.
    • medial prefrontal cortex may monitor forms of conflict at stages of processing other than response generation.
    • Dorsomedial prefrontal activation is greatest when subjects choose not to guess, not detecting of errors.
    • Posterior cingulate cortex may also contribute to the ERN.
    • Dorsomedial prefrontal cortex activation recasts as a mismatch between new information and expectations.
    • Results suggest that conflict monitoring is not necessary for error detection.
    • Functional Organization of Dorsomedial Prefrontal Cortex
    • Cingulate sulcus shows increased activation in response to difficult judgments.
    • Increasingly complex sorts of control processes evoke activation in progressively more anterior regions.
    • Incompatibility between potential responses evokes fMRI activation in the most posterior region.
      Difficulty of choosing between options evokes activation in a middle region.
      Deviations from an ongoing decision strategy evoke activation in the most anterior region.
    • Topographical gradient has similarities to that postulated for the lateral surface of the prefrontal cortex.
    • Relating the medial and lateral prefrontal cortices within larger networks.
    • Working Memory: Maintaining Information and Rules over Time
    • Temporary maintenance and manipulation of information necessary for achieving short-term behavioral objectives.
    • Involves transiently activating sensory representations.
    • Alan Baddeley model: Three capacity-limited memory buffers (phonological loop, visuospatial sketchpad, episodic buffer) and a central executive.
    • Nelson Cowan model: Two embedded levels of working memory: long-term memory representations in an “activated state” and activated representations within the focus of executive control.