Executive Function (Cognitive Control)

Executive Function and the Prefrontal Cortex

• Executive function and the prefrontal cortex
• Controlled vs automatic behavior
• Inhibition
• Monitoring
• Switching/set-shifting
• Goal-directed behavior
• Maintenance in working memory
• Sequencing steps; planning
• Improving executive function

What is Executive Function?

• Executive function is a constellation of abilities related to higher-order behavior.
• It involves guiding actions, perceptions, and thoughts in a goal-directed manner.
• Executive function is also referred to as cognitive control, which is the control of behavior in pursuit of goals.

Prefrontal Cortex and Executive Function

• Damage to the prefrontal cortex (PFC) is associated with characteristic deficits.
  • Observed by Bianchi (1922), Luria (1966), and Duncan (1986).
• Deficits include:
  • Disorganized, fragmented, and purposeless behavior.
  • Failure to complete sequences of actions.
  • Inability to approach complex tasks with planning and strategy.
  • Failure to correct errors or fully appreciate them.
  • Inclusion of irrelevant information in responses.

Phineas Gage Case

• Phineas Gage (1848) was an early prominent case of frontal lobe damage leading to disruption in organized/contextually-appropriate’ behavior
• Harlow, 1868: The equilibrium or balance, so to speak, between his intellectual faculties and animal propensities, seems to have been destroyed. He is fitful, irreverent, indulging at times in the grossest profanity (which was not previously his custom), manifesting but little deference for his fellows, impatient of restraint or advice when it conflicts with his desires…”

Major Divisions of the Prefrontal Cortex

• Lateral (inhibition/goal maintenance)
• Medial (monitoring)
• Orbitofrontal

Prefrontal Cortex

• The prefrontal cortex is the neural substrate of advanced cognitive abilities in humans.
• Evolutionary comparison shows increasing PFC size from squirrel monkey to human.

Controlled vs. Automatic Behavior

• Frontal lobe patients exhibit:
  • Few problems in routine situations where appropriate response/action is stimulus-driven and obvious (reflexive).
  • Difficulty inhibiting reflexive actions.

Testing Inhibition of Automatic Behavior

• Inhibition of automatic/reflexive behavior can be experimentally tested using eye movements (saccades).

Antisaccade Task

• The antisaccade task involves suppressing reflexive saccades.

Antisaccade Task and Frontal Lobe Damage

• Human patients with damage to the frontal lobes have difficulties suppressing the “reflexive” saccades.
• Typical lesion location: superior lateral frontal cortex

Superior Lateral Prefrontal Cortex

• Lesions to the superior lateral prefrontal cortex suggest it is necessary for inhibiting reflexive eye movements.
• Functional MRI shows that neural activity is correlated with this inhibition of reflexive eye movements.

Antisaccade Task and fMRI Results

• Curtis & D'Esposito, 2003: Antisaccade > Prosaccade
• Frontal areas are more active for antisaccades compared to prosaccades.
• Pre-supplementary motor area (pre-SMA) and supplementary eye fields (SEF) are involved.
• The activity difference occurs during the response period of the trial.

Prefrontal Inhibitory Control of Sensory Responses

• Knight, 1994: Lateral prefrontal cortex inhibits activity in sensory cortex when stimuli should be ignored.
• PFC patients show exaggerated responses to irrelevant stimuli.
• Scalp EEG recordings over somatosensory and auditory cortex.

Inhibitory Control of Sensory Responses - Experimental Paradigm

• Stimulus (2s) -> Instruction (800ms) -> Delay (800ms) -> Response (800ms) -> ITI (9s/10s)
• Instructions included:
  • Remember scenes, ignore faces.
  • Passively view.
  • Remember faces, ignore scenes.

Inhibitory Control of Sensory Responses - Results

• Older adults show reduced ability to inhibit PPA response in “Remember faces” condition (when scenes are irrelevant).

Performance Monitoring and Evaluation

• The medial region of the prefrontal cortex (anterior cingulate) monitors ongoing task performance to determine when cognitive control needs to be deployed.

Error-Related Negativity (ERN)

• Error-related negativity (ERN) is a scalp EEG component that emerges following errors.
• Amplitude scales with the size of the error and with emphasis (or not) on accuracy.

Flanker Task

• Incompatible trials evoke response conflict.
• Is there a brain mechanism for detecting the onset of this conflict?

Gratton Effect

• Botvinick et al., Nature (1999)
• cC = compat following compat
• cI = compat following incompat
• iI = incompat following incompat
• Dorsal anterior cingulate cortex (dACC)

Stroop Task

• ACC detects conflict between text and ink.
• Does ACC activity on trial n influence performance on trial n+1?
• ACC: anterior cingulate cortex

Stroop Task - ACC Activity

• ACC activity is greater when text and ink color don’t match (incongruent) relative to when they do match (congruent).
• Among incongruent trials, ACC activity is greater when the prior trial was congruent.
• Kerns et al., 2004

Stroop Task - Behavioral Adjustment

• High behavioral adjustment (greater speeding of reaction time from trial n to trial n+1) is associated with high ACC activity on the prior trial (trial n).

Switching/Set Shifting

• When the situation changes, people can switch behaviors to accommodate the new context.
• Frontal lobe patients have difficulty switching.
• Tested using the Wisconsin Card Sort Test.

Short-Term/Working Memory

• Executive function/cognitive control relies heavily on processes for guiding behavior in a way that is not stimulus-driven.
• Maintaining a representation of a previous stimulus (or goal) to guide behavior now.
• Working memory allows maintenance of a limited amount of information for a short time while actively working on it.
  • Example: Rehearsing a phone number or keeping in mind the current step of a recipe.

PFC Damage Impairs Short-Term Maintenance

• Jacobson, 1936: If a delay was interspersed between the Cue and Response periods, lesioned animals could not correctly identify the well with the food
• Only for PFC lesions
• Macaque with PFC lesion.

PFC Neurons Show Delay Period Firing

• Recordings from neurons in PFC show increased activity during delay periods when task-relevant information must be maintained.
• Fuster & Alexander, 1971; Funahashi et al., 1989

Persistent Activity in PFC Neurons

• PFC neuron with memoranda in its receptive field.
• PFC neuron with memoranda outside its receptive field.

PFC Damage Impairs Completion of Multi-Level Goals

• Achieving multi-step goals requires maintaining information in mind (working memory) and sequencing steps.
• PFC patients have difficulty achieving multi-step goals and with sequence generation/memory.

Tower of Hanoi Task

• Tower of Hanoi task evokes PFC activity with increasing difficulty.
• PFC patients have difficulty with the Tower of Hanoi task.

Improving Executive Function

• Executive function/cognitive control allows for flexible use of task-relevant information in order to act appropriately to the context.
• Resolving stimulus and response conflict.
• Guiding abstract, goal-oriented behavior.
• Maintaining information in working memory.
• Can these abilities be trained?

Video Game Training

• Video game interface to test the ‘cost’ associated with multitasking.
• Does training in multitasking lead to long-lasting improvements in ability?
• Anguera et al (2013)

Susceptibility to Distraction

• Susceptibility to distraction increases with age (presumably along w/PFC decline).
• Video game training reduced this decline and led to enhanced midline frontal lobe scalp EEG response.
• Anguera et al (2013)

Midline Frontal Effect

• The midline frontal effect may indicate that training improved older adults' ability to monitor and correct their performance following errors.
• Anguera et al (2013)
• Gratton Effect
  • cC = compat following compat
  • cI = compat following incompat

Summary

• Executive function enables flexible goal-guided behavior and depends on the prefrontal cortex.
• Controlled vs automatic behavior
• Inhibition of irrelevant representations
• Monitoring/resolving conflict
• Switching/set-shifting
• Goal-directed behavior
• Working memory delay period activity
• Sequencing steps; planning