Executive Functions PDF

Executive Functions Highly related to attention, di cult to make a clear cut distinction for certain functions WHAT ARE EXECUTIVE FUNCTIONS? Executive function: a group of global processes that allow to us to select, plan, sequence/ organize, exibly execute and evaluate behaviour - generally associ...

Executive Functions Highly related to attention, di cult to make a clear cut distinction for certain functions WHAT ARE EXECUTIVE FUNCTIONS? Executive function: a group of global processes that allow to us to select, plan, sequence/ organize, exibly execute and evaluate behaviour - generally associated with frontal (and parietal) lobes - Key capacities involved in human cognition (vs primates) - Usually is impaired when having a traumatic injury - Help us organize some sensory/motor functions Cognitive control: another way of thinking about executive function - controlled (actively allocate resources) vs automatic processing - Selecting, scheduling, switching or inhibiting CASE OF DR P - Damage to the frontal lobe during facial surgery - No change in IQ (high average) i.e. general cognitive function Impairments: - Could not plan daily activities - had to call after every delivery for instructions (even if same every day) - Needed someone to tell him to change clothes, shower (not reluctance) - Did not initiate any activities (if not prompted, wouldn’t do anything) - Unaware of his problems (no insight) - Became unsociable, showed little emotion - Did not talk or engage with those around him - Cannot plan: knows what he has to do but needs a prompt - can seem unmotivated - unable to think about now and compare to before injury - Planning network linked to reward and motivation/emotion - Cannot evaluate the outcome in relation to plan PREFRONTAL CORTEX ffi fl Hierarchy of processing: sensorimotor to abstract - PMC and vLPFC: direct sensory-motor or response associations - dLPFC: manipulating, ordering information or task - Frontal polar: switching between tasks, high level ordering - Orbital and medial frontal: evaluation of reward, novelty - SMA: sequencing - Area representing the legs, a little of the core, genitalia - ACC: error processing, inhibition - Linking between sensory and motor - Broca: also part of planning, EXECUTIVE FUNCTIONS AND GOAL-DIRECTED BEHAVIOUR - Initiating actions - Selecting and maintaining a goal - Sequencing and planning - Set shifting and modifying goals or strategies - Monitoring and evaluation - Inhibition INITIATING ACTION - People with frontal lesions have trouble initiating actions - Left hemisphere damage: reduced speech - i.e. Parkinson’s disease - Premotor cortex (PMC): Supplementary motor area (SMA) and anterior cingulate important for action initiation - BG also involved: People with Parkinson’s disease have di culty initiating movements MOTIVATION FOR ACTION EVALUATING EFFORT Study: how hard will you work for a reward - squeezing to get apples - The harder people were willing to squeeze a hand-grip, the greater was activity in ACC (as well as DLPFC and parietal) ffi - People with frontal lesions may not be able to make this evaluation - Will squeeze really hard for all and lose strength to squeeze for higher rewards - Or simply will not squeeze GOAL MAINTENANCE AND SWITCHING Receive a cue in terms of colours, then a pause, and evaluate the shape associated with or the location of where the colour was - In all conditions, premotor, SMA and parietal active when people are maintaining the goal indicated by the cue - Activity increases when people must switch, especially across categories (location/colour)/ di culty of maintaining the task set ***The more attention needed, the greater the activity VOLUNTARY SWITCHING Seeing a series of number and asking how big the number is compared to the screen (size of the font) and how big the number is (value) Frontal polar cortex is active for voluntarily switching (participant’s choice to choose) between two tasks, especially when an active voluntary choice is made Frontal polar guides all other executive functions SEQUENCING/ORDERING SEQUENCING AND PLANNING Self-ordered pointing task In humans and primates - get 6 cards and pick di erent image every time - People with frontal lesions are impaired on this task - Point to same picture repeatedly - Cannot remember the sequence/how long ago they saw a picture - dLPFC is more active when people judge how recently they saw a picture, compared to whether they saw it (recognition) - People with hippocampal lesions can judge recency, but cannot recognize the pictures - They can remember when they saw the picture last, but cannot recognize the picture Tower of London task - balls on peg with initial position that have to be moved to goal position in fewest number, moved one at a time - Participant needs to plan their moves - Performance on how fast they do/how many errors made and how many moves they make - People with frontal lesions are impaired on this task ff ffi - dLPFC and superior parietal lobule are more active for 4-move and 5-move trials - can see change in performance in those with no lesion to PFC - Make more moves - Impulsive person would perform poorly since they would not take time to plan SHIFTING GOALS AND STRATEGIES Wisconsin Card-sorting task - open ended = very demanding on the frontal lobe - Emotion regulation - Planning - Test can be sensitive to frontal lobe impairment - People must match a set of cards to one of four key cards - Di erence in shapes, colours, and numbers (can match or not match depending on researcher’s criteria) - Only get “correct” or “incorrect” as feedback - After a person has matched correctly for several trials, tester switches the rule, and the person must learn again - People have to strategize, ignore irrelevant information, switch, learn from feedback, retrieve and monitor working memory - People with frontal lobe damage, especially to dLPFC, do poorly on this task - People with SCZ also showed impairment - dLPFC is active during this task, especially when people decide whether to switch or stay - Left dLPFC damage seems to impair switching - Facilitory TMS over left dLPFC improves performance - Right dLPFC damage impairs inhibitory control - maintaining set in the face of interference MONITORING AND EVALUATION Error-related negativity Moving cursor to a target - if mistake is made = negative ERP - A negative ERP occurring 100 msec after the error - ERN is greater when people are told to emphasize accuracy, smaller when they emphasize speed - The ERN is generated in the ACC - AAC may be important for computing errors - Identifying con ict - Evaluating error for learning INHIBITION Go/No go task - More “go” than “no-go” trials, so must inhibit a response on “no-go” trials fl ff Stop signal - Must stop a response that is already underway fl - Both tasks engage frontal, parietal, SMA and ACC - Similar to tasks requiring con ict resolution or task switching