what is executive function
- not perception, action attention, LTM, language, deacon making, or emotion, but effects all of them
- guides and coordinates all processes in service to our plans and goals
- it is cognitive control, emotional control, executive control, self control
homunculus is control
- stop appealing to an ill defined and circular self, central executive, or consciousness to explain goal-oriented behaviour
- a mechanistic account of executive function in neural, psychological and computational terms
components of executive function
- working memory maintenance( what have i tried?)
- working memory updating (remembering previous trials)
- inhibition of prepotent actions (don’t sort by rules seen before)
- shifting between rules, sets, and tasks (try each rule until one works)
- monitoring and adjusting performance (detect when rule is no longer working and adjust)
effect of prefrontal cortex lesions : perseveration
- repetition of a particular response
- in task: sticking with a rule when it is no longer working
- failure of monitoring, updating, shifting
effect of prefrontal cortex lesions : impulsiveness
- inability to stay focused on current task set
- in task: jumping between rules in a disorganized way
- failure of maintenance, inhibition
oculomotor delayed response, task
- performed by monkeys
- single-cell recording in dorsolateral prefrontal cortex (DLPFC)
- responses of a single DLPFC neuron differ for cue locations
- spatial tuning curves for 4 different DLPFC neurons during delay period
- DLPFC fires in correct trials, and less in error trials, especially in cue locations
DLPFC : working memory maintenance
- is DLPFC delay period activity necessary for memory performance?
- create focal lesions in unilateral left DLPFC
- 2 tasks: oculomotor delayed response (memory) and visually guided saccade task (control)
dorsolateral prefrontal cortex neurons
- delay period activity
- directionally tunes
- lasts for duration of delay
- predicts memory performance
- damage to specific neurons impairs short term memory for corresponding locations
stroop task
read either word or name ink colour
stroop effect
- when colour words and ink colours conflict, colour words are much harder to ignore than ink colours
- hard b/c more practice with word reading than colour naming
- overcome : inhibition of prepotent response
stroop network model
- neural network model layers
- visual perception
- perceptual-motor mapping
- verbal response
- goal maintenance/cognitive control
how is inhibition implemented?
- goal representations maintained in dorsolateral prefrontal cortex provide top-down biasing of perceptual-motor mappings
- working memory provides the signal
- inhibition is the effect
eriksen flanker task
- respond to the central letter surrounded by flankers
flanker effect
incongruent trials are slower than congruent trials
- require top-down control
gratton effect
the flanker effect is smaller after incongruent trials than after congruent trials
- when need-for-control detected on previous trial, more control is applied on current trial
ACC performance monitoring
- monitors performance: detects errors, detects response conflict, signals need for control to DLPFC
- other roles: signals prediction error, selects among possible actions
orbital frontal cortex: value based control
- integrates value single from multiple sources: DLPFC (task relevance), Amygdala (reward value), Insula (anticipated outcome)
- uses resulting call-signal to guide goal-oriented behaviour
1-2-AX task
- see sequence of letters and digits
- press left button for each except
- press right button for X preceded by A, if most recent number was 1
- press right button for Y preceded by B, is most recent number was 2
model of executive basal ganglia loop
1-2-AX task
- need to maintain multiple items (1, 2, A, B)
- update specific items
- ignore other items
- use memory to control performance
- learn when/what to maintain, store, ignore, forget
basal ganglia: learning to control from reinforcement
- basal ganglia uses dopamine-based reinforcement learning to learn when to take actions
- working memory updating = internally -directed action selection
- basal ganglia helps PFC learn when and how to apply executive control
rostral/caudal: abstraction
- rostral PFC: complex, abstract, long timeframe
- caudal PFC: simple, concrete, short timeframe
rostral/caudal: abstraction alley-oop example
rostral - what sport am i playing? (basketball) - what position am i playing? (forward) - what play are we running? (alley-oop) Caudal What do i need to do next? (JUMP)
ventral/dorsal: what and why VS where and how
ventral PFC: what, why, meaning oriented
dorsal PFC: where, how, action oriented
ventral/dorsal: alley-oop example
Ventral
- what am i doing and why? ( on offence, need to put ball through hoop to score)
Dorsal
- how do i do it, and where should i be? ( approaching basket, catch ball at apex, slam it through hoop)
