Orbitofrontal Cortex & Executive Function

Question 1

OFC vs PFC

Answer 1

• general consensus = regions in lateral/medial PFC (DLPFC/VLPFC/ACC) are doing something dif from orbitofrontal cortex (OFC)
• aka. cold VS hot cognition

Question 2

BECHARA ET AL. (1994): PROCEDURE

Answer 2

• looked at role of orbitofrontal cortex in cognitive control via IOWA gambling task
• pps presented w/4 virtual card decks on computer screen; told that each time they choose a card they’ll win game money BUT sometimes choosing a card loses money
• game goal = win as much as possible
• decks differ in trial numbers over which losses are distributed aka. some decks = “bad”/”good” as they’ll lead to eventual loss/win

Question 3

BECHARA ET AL. (1994): RESULTS

Answer 3

• normal controls learned to avoid risky decks & chose decks w/overall profit
• patients w/lesions to occipital/temporal/dorsolateral prefrontal cortical regions = equivalent performance (usually preferring “good” decks)
• BUT patients w/OFC lesions = pref for risky decks aka. unable to learn about response-reward contingencies

Question 4

BECHARA ET AL. (1996)

Answer 4

• tested skin conductance response (SCR) of OFC lesion patients performing same card-game task from previous studies
• SCR = sweating measure checking anxiety
• SCRs during reward/punishment = roughly equivalent in patients/controls
• BUT anticipatory SCRs (measured between deck choice & receipt of reward/punishment) = greatly reduced in patients w/OFC lesions

Question 5

DAMASIO: SOMATIC MARKER HYPOTHESIS

Answer 5

• focus on OFC role in value-based decision making
• emotional info (as physiological arousal) is needed to guide decision making
• somatic markers = bodily reactions to emotional stimuli
• OFC supports learning of associations between somatic markers/complex situations
• OFC can use said info to access likely outcomes of beh choices

Question 6

IOWA GAMBLING TASK (IGT): LIMITATIONS

Answer 6

• cards = presented in fixed order inducing pref for risky decks (aka. wins experienced early; losses experienced later)
• pps must overcome said pref & switch to “good” decks to perform well on task
• this inhibition/switching process = reversal learning

Question 7

FELLOWS & FARAH (2005)

Answer 7

• standard IGT = risky deck loss experienced later (reversal learning required)
• variant IGT = risky deck loss experienced earlier (no reversal learning)
  RESULTS
• VMF patients = impaired relative to controls on standard IGT
• impairment disappears in variant IGT
• suggests deficit is in reversal learning > broad value-based decision making

Question 8

FELLOWS & FARAH (2003): PROCEDURE

Answer 8

• further investigated previse role of OFC in value-based decision making
• reversal learning task = pps learned which card predicts reward then contingencies shifted
• included patients w/DLPFC/ventromedial (OFC) lesions

Question 9

FELLOWS & FARAH (2005): RESULTS

Answer 9

• DLPFC = unimpaired
• OFC = specific deficit at reversal stage
• could learn initial response contingencies BUT had issues learning about new contingency
• researchers argued that OFC = necessary NOT for learning about stimulus-reward contingencies but for unlearning established associations

Question 10

O’DOHERTY ET AL. (2001): PROCEDURE

Answer 10

• neuroimaging evidence supporting that OFC may be divided according to dif functions
• pps performed probabilistic reversal learning task; rewarded for choosing 1 reward but punished for choosing the other
• contingencies changed post learning reward option; had to learn responses to other stimulus

Question 11

O’DOHERTY ET AL. (2001): RESULTS

Answer 11

• dissociable regions of OFC responded preferentially to rewards/punishments:
  1) medial OFC = stronger response to reward
  2) lateral OFC = stronger response during punishment (just pre reversal)
• suggests that dif regions in OFC respond to dif outcome types

Question 12

CHUDASAMA ET AL. (2017): PROCEDURE

Answer 12

• limitation for reversal learning hypothesis
• monkeys w/OFC lesions don’t always show reversal learning deficit
• monkeys had to select large/small reward (ie. 4 peanuts VS 1 peanut) aka:
  1) selecting small reward -> gives big reward
  2) selecting big reward -> small reward
• task requires overcoming innate pref for larger food rewards aka. dif to standard reversal learning task involving learning/suppression of arbitrary stimulus-outcome relations

Question 13

CHUDASAMA ET AL. (2017): RESULTS

Answer 13

• monkeys took long time to learn task (50 sessions)
• reversal learning takes place over much shorter time periods
• aka. OFC may only be required for reversal learning when stimulus-outcome computations = made “on-the-fly” & suppression involved arbitrary stimulus-outcome relations

Question 14

OFC: COMPUTATION VALUE

Answer 14

• recent OFC function POVs emphasise computation value
• OFC = “accountant” converting info about outcomes (prob/magnitude/costs/etc) into “common neural currency” on which to base choices
• may account for OFC role in generation of complex emotions (ie. regret)

Question 15

CAMILLE ET AL. (2004): PROCEDURE

Answer 15

• OFC x neglect
• pps chose 1/2 wheels w/dif winning chances
• either got:
  1) partial feedback (found out they won & know possibilities if they chose other wheel BUT don’t know what they’d’ve won if they chose the other)
  2) full feedback (found out what they won & what they would’ve won if they’d chosen other option)
• asked pps to rate satisfaction lvl upon outcome

Question 16

CAMILLE ET AL. (2004): RESULTS

Answer 16

• healthy pps:
  1) ^ satisfaction ratings upon finding out they’d’ve won less/lost more if they’d’vechosen other wheel
  2) lower ratings when they’d’ve won more/lost less if they’d’ve chosen other wheel
• OFC patients didn’t show this counterfactual thinking pattern aka. didn’t modulate ratings according to if alternative wheel would be win/lose
• suggests key role of OFC in experiences winning/losing consequences & (importantly) integrating info from dif outcome sources

Question 17

SUMMARY

Answer 17

• facilitating effective decision making based on knowledge of value of dif actions
• suppressing actions based on recently learned action-outcome relations
• only seems necessary for value computations when based on new info that changed rapidly
• ability to “mentally stimulate” info about predicted outcomes = key