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PSY2303 Cognition and Emotion > PFC > Flashcards

Flashcards in PFC Deck (54)
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1

PFC

Must be doing something imp to distinguish us from other animals

see notes

Shows development trajectory of brain devel between 5-20

Scale shows density of gray matter across brain

Thins over whole brain

Biggest changes in red region – PFC

see notes

2

connections of the frontal cortex

Connected to most regions – role in behav

see notes

3

Phineas Gage

“The equilibrium or balance…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, at times obstinate, yet capricious and vacillating, devising many plans of future operations, which are no sooner arranged than they are abandoned in turn for others appearing more feasible. …

In this regard his mind was radically changed, so decidedly that his friends and acquaintances said he was "no longer Gage”

4

Wisconsin Card Sorting Task

Set shifting task

Set = approach to a problem

Given single card and must choose which of 4 decks to place card on

Have to learn rule governing which deck should be placed on and continue to place diff cards on same deck according to correct rule

Rule could be based on colour, shape, no. of shapes etc

Patients must use trial and error to find correct rule

After 10 consecutive correct responses, rule changed and patient must discover new rule

Task-set switching/shifting

Must acquire ‘set’ for task perf = rule/set of rules

Set can switch repeatedly throughout task

see notes

5

errors on WCST pre- and post-surgery - Milner (1963)

Deficit of inhib (inhib previously relevant ‘set’ and responding appropriately using currently relevant set)

Those w/ frontal lobe injuries showed disproportionate impairment on task

Perseverated – after rule changed, tended to carry on responding according to same rule

Conclusion that PFC doing something related to inhibition – enabling flexible behav by inhibiting (suppressing) previously relevant, but no longer relevant, responses

see notes

6

Shallice and Burgess

Patients with frontal lesions often perform normally on ‘frontal’ tasks such as Wisconsin Card Sorting Task

Still fail at simple tasks such as going to shops
o Disconnect
o Deficit may be more complex than previously thought

7

deficits of patients w/ frontal lobe lesions on standard neuropsych tasks - Shallice and Burgess (1991)

Patients w/ frontal lobe lesions not v. impaired on tasks that measure frontal exec functions

E.g. Stroop task (attentional interference), Tower of London task (planning), even modified WCST

see notes

8

six elements task - Shallice and Burgess (1991)

Limited total time (e.g. 10 mins)

6 diff tasks to work on, such as picture naming, arithmetic, visual cancellation task

Goal is to work on all 6, and hopefully complete all 6 in 10 mins

Score based on no. tasks attempted, and score penalties given for rule infractions/not spending equal amount of time on each task

9

deficits of patients w/ frontal lobe lesions on the six elements task

“The problem arose from an inability to reactivate after a delay previously generated intentions when they are not directly signalled by the stimulus situation….

These processes lie in the domain of the creation and maintenance of goals and intentions, of their realization at appropriate times (prospective memory) and of planning…where a task cannot be adequately carried out through the application of well-learned action or thought routines alone, it requires the use of a Supervisory System, which is anteriorly located in the cortex”

Only attempted 2/3 of tasks and spent large amount of time on each sub-tasks

Deficits due to breakdown in unitary supervisory system, located in PFC

Worse on tasks that mirror real-life

see notes

10

the SAS model - Norman and Shallice (1980)

Supervisory Attentional System

Explains how behav can operate in non-routine situ’s – where well learned behav sequences not sufficient

WCST could been seen to be model of type of behav – patient leanrs rule governing responding but then has to re-learn rule repeatedly

see notes

11

problems with the SAS

‘Homunculus’ criticism

Who controls controller?
o Problem then is how second system is controlled

Explains what is controlled but not how control exercised
o Black box without any attempt to explain how it carries out its function
 Very influential in psych
 Control system in PFC used as explanation in neuropsychiatric disorders
 Addiction/ADHD/Sz can be partly explained by deficit in PFC control systems
 All it does is re-describe behav symptoms using diff (technical) words

12

fractionating exec function - Monsell and Driver (2000); Verbruggen et al. (2014)

“Dissolve, deconstruct/fractionate executive! Let a hundred idiots flourish”
o Identify basic cog processes underlying cog (behav data – FA)
 Can produce coord, goal-directed behav through coord functioning
 Identify underlying common and distinct variables that diff tasks rely on further idea that should be possible to identify diff regions of PFC that are responsible for controlling diff cog processes, through neuropsych and neuroimaging
o Identify diff brain regions underlying different cog control processes (neuropsych/neuroimaging)
o Fractionate SAS into many component processes

13

subdivisions of the PFC

Some broad agreement

see notes

14

how can we fractionate exec function at the behav level? - Miyake et al. (2000)

Gave healthy subjects variety of tasks:
o E.g. task switching – subjects have to perf 2 tasks – odd/even or vowel/consonant – depending on location of letter/numbers
o Slower in switch trials than are in repeat trials on task

15

FA of exec function - Miyake et al. (2000)

3 distinct, latent variables that accounted for perf diffs on 9 tasks

Variables (/factors) shown in central part
o Shifting = shifting between task sets
o Updating = updating contents of WM
o Inhib = inhib prepotent responses

Influential model – used as template for understanding how exec functions can be fractionated

Idea that any complex exec task can be accomplished by drawing on (mixture of) 3 functions

Real test is whether can map these diff functions onto diff brain regions

see notes

16

is there a dysexecutive syndrome? - Stuss and Alexander (2007)

“Our goal was to determine whether all focal frontal lesions produced a similar impairment in cognitive supervisory control or whether lesions in different regions produced specific impairments that might or might not appear on a task depending upon the particular demands of the task.”

Tested frontal lobe patients (n = 40) on range neuropsych tasks inc. classic frontal tasks (WCST, Stroop), language and memory tests requiring exec functions and attentional tests

Brain lesions mapped out and location of brain damage defined by registration to standard anatomical template

17

neuropsych ev - Stuss (2007)

Right lateral PFC
o Monitoring
o Process of checking task over time for ‘quality control’ and adjustment of behav
o Miyake’s “updating”

Left lateral PFC
o Task setting
o Ability to set stim-response r’ship
o ‘Shifting”

Left medial PFC
o Energising
o Process of initiation and sustaining of any response

Where is inhib?
o Stuss suggests it may not exist at psych level/not necessary component to explain perf on tasks used

see notes

18

medial PFC - the view from neuroimaging - Carter et al. (1998)

Stuss = ‘energising’

ACC as “error detection" module?

Asked healthy subjects to perf ‘AX-CPT’ task (continuous perf task) in MRI scanner

See 2 letters on each trial, one after other

First can be A/B and second can be X/Y

Press button when see X but only when preceded by A

Leads to high error rates because on some trials see A which primes them to make response, but then see Y – press accidentally

Measure brain activation during error and correct trials and found increased activation in ACC for errors relative to correct trials

see notes

19

medial PFC - the view from neuroimaging - Bush et al. (1998)

fMRI - counting Stroop

say how many words were on screen on each trial

Interference (word 2 when 4 words on screen) v neutral trials (dog)

ACC activation higher in interference than neutral trials even when subject responded correctly

ACC involved in conflict detection

Tasks that require resolution of conflicts between competing info streams by sensory and/ response selection

Results inconsistent with previous study as show ACC activation not simply associated with errors

Suggests error-related activation occurs because of detection of conflict between competing info streams

On error trials, conflict arises due to mismatch between subject’s expectation that they got trial correct, and incorrect feedback they actually receive

see notes

20

role of the medial PFC in cog control

Neuroimaging inconsistent with lesion ev
o Bush/Carter – ACC activation related to conflict monitoring
o Stuss – ‘energising’ behav

Possible role for ACC in evaluating effort associated with a choice
o Grinband et al. (2008) – Stroop task
 ACC activation linked to time-on-task – greater activation for slow RTs than fast even on congruent trials
 Potential resolution to inconsistency
 ACC sensitive to amount of effort involved in task perf

see notes

21

left lateral PFC - the view from neuroimaging - Kim et al. (2012)

Results of meta-analysis of 36 task switching studies
o Compared switch trials v no switch trials
o Bilateral pattern of activation, distributed across frontal and parietal regions – greater activation for switch trials than non-switch trials
o DLPFC preferentially left lateralised
o Some convergence w/ neuropsych ev but suggests more distributed network involved

22

further neuroimaging evidence suggesting a role for parietal cortex in task-switching – decoding of task rules from patterns of activation in lateral PFC and parietal cortex - Bode et al. (2009)

see notes

Analysed fRMI data with MVPA method – decoding cog states from patters of activation

Gave subject task-switching task in which subjects saw cue (letter A/B), followed by 1 of 2 coloured patterns

If cue was A, subject had to make left button press response for pattern 1 and right button press response for 2

If cue B, had to flip stim-response association and make right button press for 1 and left for 2

Used pattern classifier

Found task rules could be decoded from parietal and PFC

Line graphs - bin 1 = cue presentation, bin 3 = target presentation, bin 5 = response)

Top graph shows decoding perf for region in parietal cortex (left intraparietal sulcus)

Bottom graphs show decoding perf for regions in PFC

Successful decoding of task earliest in parietal region (before target presented) whereas task could only be decoded later in trial from PFC activation (after target presentation)

23

left lateral PFC - view from neuroimaging

Partial support for the Stuss idea that left lateral PFC involved in task setting/switching

Neuroimaging reveals more distributed system inc. right lateral PFC and inferior parietal cortex

Possibly key role for parietal cortex

24

right lateral PFC - ev from neuropsych

Stuss: monitoring – process of checking the task over time for ‘quality control’ and adjustment of behav

Aron et al. (2003) demo’d imp of right inferior frontal cortex for response inhib

Gave Ps w/ diff brain lesions Stop Signal RT task in which had to respond whether arrow was pointing to left/right but sometimes had to withhold response when heard loud beep

Found perf strongly related to size of lesion in right inferior frontal gyrus – pos correlation between Stop Signal RT (measure of how good subject is at inhib response) and lesion size in region – bigger lesion, worse at inhib

see notes

25

right lateral PFC - ev from neuroimaging

Imaging studies supported findings, showing increased activation in right inferior frontal cortex during response inhib

see notes

Many studies put healthy people in scanner and given them go/no-go tasks in which subject simply has to press key when see certain letters and withhold responding when see diff letter

Activation in right inferior frontal cortex higher for no-go trials than for go, suggesting specific role in region in inhib prepotent response

26

right lateral PFC - ev from neuroimaging - Hampshire et al. (2010)

More recent research suggests this may be due to an attentional role for the right inferior frontal cortex

In go/no-go tasks and stop-signal tasks, subject must monitor for occurrence of ‘target’ stim that indicates should withhold response

Strong attentional component, requiring target detection

Possible that activation in inferior frontal cortex during tasks actually reflects more basic target detection processes rather than response inhib

Gave subjects v. simple task in which required to monitor for occasional targets and found increased activation in right inferior frontal gyrus (and less extent left) when detected target

More basic attentional role

see notes

27

convergence of ev

Some agreement between behav, neuropsych and neuroimaging ev for how to fractionate PFC

Also disagreement:
o Functions carried out by regions not v. precisely specified – disagreement about what specific regions ‘do’ e.g. right inferior frontal cortex
o Neuroimaging generally implicates wider networks of regions other than just PFC
o Even existence of certain exec functions (e.g. inhib) point of debate

28

methodological considerations may partially account for lack of convergence

Neuroimaging methods show regions generally involved in task perf, not necessarily those necessary for task perf

Neuropsych reveals regions that are necessary for task perf but cannot reveal info about networks of brain regions

Is it possible to fractionate PFC?

29

an alternative perspective from neuroimaging – frontoparietal cortex as a ‘multiple demand’ network - Duncan and Owen (2000)

Meta-analysis of neuroimaging studies of exec function, in which plotted activations associated w/ multiple diff processes, e.g. response conflict, task novelty, on single brain

Rather than there being separate regions of PFC dedicated to diff processes, diff processes all activated similar regions

No clear separation between diff processes – more like there was network of regions, encompassing regions in lateral PFC, anterior insula, medial PFC and inferior parietal cortex, that all showed increased activation when Ps did something cog difficult

Called frontoparietal ‘multiple demand’ network

see notes

30

what does the 'multiple demand' network do?

Construction of ‘attentional episodes’

“Neurons have highly dynamic response properties, adapting to code the specific information and events within the current attentional focus”

“With the transition between one episode and the next, neural coalitions for one kind of information processing dissolve and coalitions for the next episode form, producing a system in constant flux.”

Adaptive coding – PFC neurons adapting responses depending on task demands