The Frontal Lobes Flashcards
PREFRONTAL CORTEX (PFC)
- very front part of brain
- largest in humans
- similar to chimps BUT there’s a lot more complexity in folds (sulci/gyri of human brain)
- must be doing something important to distinguish us from other animals as connected to every other region of brain so suggests it plays a key role in human beh
AGES 5-20: DEVELOPMENTAL TRAJECTORY
- grey matter thins out over whole brain w/age
- BUT some biggest changes appear to happen in red region (frontal lobe)
- aka. frontal lobe must be doing something important related to beh changes we see childhood -> adulthood
FRONTOSTRIATAL LOOPS
- some strongest connections occur between regions in PFC & basal ganglia (striatum) aka. collection of old/subcortical structures incl. caudate/putamen/globus pallidus/ventral striatum
- loops seem to occur in parallel w/dif loops connecting dif PFC regions
- hypothesised to play dif roles ie. reward processing loop connecting ventral striatum to OFC & executive control loop connecting DLPFC to dorsal striatum
FRONTAL LOBE: ANATOMY
LATERAL SURFACE
- lateral frontopolar cortex (BA10)
- dorsolateral prefrontal cortex (BA9/46)
- anterior premotor cortex (BA8)
- premotor cortex (BA6)
- primary motor cortex (BA4)
- ventral anterior premotor cortex (BA 44/6)
- ventrolateral prefrontal cortex (BA 47/45/44)
MEDIAL SURFACE
- anterior cingulate cortex (ACC)
PHINEAS GAGE (1823-1860)
- provided 1st indications of PFC function
- metal bar shot through face & exited via skull
- survived; could speak/interact/act as normal
- BUT suffered some serious personality/control/organisation issues
RYLAND (1939)
FRONTAL LOBE/DYSEXECUTIVE SYNDROME
- characterised issues faced by patients w/frontal lobe injuries as dysexecutive syndrome involving issues w/:
1) attention (easily distracted)
2) abstraction (issues grasping whole of complicated set of affairs)
3) novelty (ok w/routine BUT issues in novel situations)
NORMAN & SHALLICE (1980)
SUPERVISORY ATTENTION SYSTEM (SAS)
- system in charge of action control & coping w/novelty
- required in situations where routine selection of actions = unsatisfactory aka. cognitive control/executive function required
CLASSIC EXECUTIVE FUNCTION TASKS
WISCONSIN CARD SORTING TASK
STROOP TASK
TOWER OF LONDON TASK
WISCONSIN CARD SORTING TASK
- shows issues frontal lobe patients have w/classic executive function
- patients given single card; must choose which 4 decks to place card on; have to learn rule governing which deck it should be placed on; continue to play dif cards on same desk according to correct rule
- rule could be based on colour/shape/number
- patient must use trial/error to find correct rule
- 10 consecutive correct responses -> changed rule; patient must discover new rule
- process oft referred to as task-set switching/shifting aka. patient must acquire set for task performance (aka. rule (set)); this can switch repeatedly during task
SUPERVISORY ATTENTION SYSTEM THEORY: EVALUATION
1) homunculus criticism
- aka. who controls the controller?
- explains what is controlled but NOT how control is exercised
2) patients w/frontal lesions tend to perform poorly on complex tasks requiring dif cognitive processes
- ie. WCST: planning/set-shifting/inhibition/selective attention/WM
- unknown which processes = actually affected
SUPERVISORY ATTENTION SYSTEM THEORY: NEXT STEPS
1) can we fractionate executive function into component processes at beh lvl?
2) to what extent can dif executive functions be mapped onto anatomically discrete locations in PFC (focusing on response inhibition)?
MIYAKE ET AL. (2000): PROCEDURE
- attempted to fractionate executive function into component variables using beh tasks/factor analysis
- gave healthy pps 9 tasks measuring variety of dif executive functions
MIYAKE ET AL. (2000): TASK I
1) task-switching
- pps had to perform 2 tasks (depending on letter/number location): odd/even OR vowel/consonant
RESULTS
- pps = slower in switch trials > repeat trials
MIYAKE ET AL. (2000): TASK II
2) letter memory task (WM)
- pps had to remember letters & also update letters in memory
MIYAKE ET AL. (2000): TASK III
3) stop signal reaction time task
- pps had to withhold prepotent responses
- task = respond as quickly as possible to direction of arrow BUT withdraw responding if you hear loud beep post arrow presence
MIYAKE ET AL. (2000): FACTOR ANALYSIS RESULTS
- 3 distinct latent variables accounting for performance difs on 9 tasks:
1) shifting (between task sets)
2) updating (updating WM contents)
3) inhibition (inhibiting prepotent responses)
MIYAKE ET AL. (2000): IMPLICATIONS
- influential model of executive function; usually used as template for understanding how executive functions can be fractionated
- any complex executive task can be accomplished by drawing on mixture of main 3 functions (shifting/updating/inhibition)
- BUT real test of trying to fractionate executive function = if we can map dif functions onto dif brain regions
COLD COGNITION
- functions that DON’T involve emotional/value-based judgements
- response inhibition
- task switching
- error monitoring
- attention
- WM
HOT COGNITION
- functions that DO involve emotional/value-based judgements
- value-based/emotion-guided decision making
- counterfactual thinking
- gambling
STRUSS & ALEXANDER (2007): PROCEDURE
- goal to determine if:
1) all focal frontal lesions produce similar impairment in cognitive supervisory control
2) lesions in dif regions produce specific impairments that might (not) appear on task depending upon its particular demands - tested 40 frontal lobe patients on range of neuropsychological tasks incl. classic frontal tasks (WCST/Stroop)/language & memory tests (requiring executive functions)/attentional tests
- brain lesions mapped out; brain damage defined by registration to standard anatomical template
STRUSS & ALEXANDER (2007): RESULTS
- found both correspondences/difs between Miyake model & patients
1) RIGHT LATERAL = monitoring (Miyake’s “updating” variable included monitoring tasks)
2) LEFT LATERAL = task setting (necessary for shifting as in Miyake) - convergence in medial PFC = energising
- no space for inhibition aka. inhibition may not exist at psychological lvl as wasn’t necessary to explain performance on used tasks
BEHAVIOURAL x NEUROPSYCHOLOGICAL EVIDENCE RELATIONS
- some agreement (ie. task setting < left lateral PFC)
- BUT some disagreement on fundamentals (ie. existence of specific components ie. response inhibition)
- so is there a response inhibition module in PFC?
ARON ET AL. (2003): PROCEDURE
- demonstrated particular importance of right inferior frontal cortex (esp. right interior frontal gyrus) for response inhibition (withholding prepotent/inappropriate response)
- gave patients w/dif brain lesions Stop Signal Reaction Time task; had to respond if arrow was pointing left/right BUT occasionally withhold response post hearing loud beep on some trials
ARON ET AL. (2003): RESULTS
- performance = strongly related to size of lesion in right inferior frontal gyrus
- aka. positive correlation between SSRT (measure of how good pp is at inhibiting responses) & lesion size (bigger = worse at inhibition) in said region
RIGHT FRONTAL CORTEX x INHIBITION: FURTHER EVIDENCE
- fMRI studies have supported Aron et al. (2003) showing ^ activation in right inferior frontal cortex during response inhibition
- many studies put healthy pps in scanner w/go/no-go tasks where pp had to press key when they see certain letters & withhold responding when seeing a certain letter (ie. X)
- activation in right inferior frontal cortex = consistently ^ for no-go trials > go trials
- suggests specific role for region in inhibiting prepotent responses
RIGHT FRONTAL CORTEX x INHIBITION: FURTHER EVIDENCE (EXAMPLES)
KAWASHIMA ET AL. (1996)
GARAVAN ET AL. (1999)
KONISHI ET AL. (1999)
MENON ET AL. (2001)
RUBIA ET AL. (2001)
KELLY ET AL. (2004)
LI ET AL. (2006)
LEUNG ET AL. (2007)
HAMPSHIRE ET AL. (2010)
DODDS ET AL. (2011)
DUNCAN & OWEN (2000): PROCEDURE
- didn’t agree that it’s possible to fractionate prefrontal cortex into separate executive processes
- meta-analysis of neuroimaging studies of executive function
- plotted activations associated w/multiple dif processes (ie. response conflict/task novelty on single brain)
DUNCAN & OWEN (2000): RESULTS
- dif processes all activated remarkably similar regions rather than separate regions of PFC being dedicated to dif processes
- no clear separation between dif processes
- rather region network encompassing regions in lateral PFC/anterior insula/medial PFC/interior parietal cortex; all showed ^ activation when pps did something cognitively difficult
- network dubbed: frontoparietal “multiple demand” network; reflects idea that it underlies cognitive performance in multiple dif demanding task types
WOOLGAR ET AL. (2011): PROCEDURE
- PFC may perform slightly more complex role
- pps had to perform task where they had to learn dif rules mapping locations to responses
- aka. when pps saw blue screen they had to remember particular mapping between locations/button presses
- BUT when pps saw pink screen they had to remember a dif mapping
- used multivoxel pattern analysis to see which brain areas encoded dif info about task (ie. rules/colours/responses)
WOOLGAR ET AL. (2011): RESULTS
- frontal/parietal regions showed strongest coding of rules despite also encoding info about stimuli position/colours/responses
- aka. demonstrates that primary PFC role in this task type = encoding info about abstract task performance aspects ie. rules governing stimulus-response mappings
- so could be claimed that these regions aren’t simply directing attention to specific stimuli in WM but also performing more complex function
MULTIPLE DEMAND NETWORK
- construction of attentional episodes
- neurons have highly dynamic response properties aka. adapt to code specific info/events in current attentional focus
- neural coalitions for 1 info type processing dissolve w/transition between 1 episode to next -> coalitions for next episode form aka. produce system in constant flux
- adaptive coding = PFC neurons adapting responses depending on task demands
RIGHT INFERIOR LATERAL PFC: SUMMARY
- may play important role in response inhibition
- BUT this may be due to role in attention
- may form part of more extended frontoparietal multiple demand network recruited whenever a task is cognitively demanding
SUMMARY
- PFC = key role in organised goal-directed beh
- some evidence that PFC can be fractionated into dif functions BUT also disagreement
- multiple demand network hypothesis offers alternative POV aka. integrated network involved in performing multiple cognitively demanding tasks
