W9.1 (C): Prefrontal cortex Flashcards
(17 cards)
What brain regions is the PFC connected to?
Virtually every other region in the brain- highly important!
Strongest connections are between regions of the PFC and basal ganglia inc striatum- there are loops which occur in parallel- diff loops connect diff PFC regions and play diff roles e.g. reward processing loop that connects ventral striatum to the OFC and an exec control loop that connects the DLPFC to dorsal striatum
What three surfaces are there on the frontal lobe/PFC?
Lateral surface
Medial surface
Orbital surface
Where did one of the first indications of the PFC function come from?
Phineas Gage
What did Ryland (1939) characterise as frontal lobe or ‘dysexecutive’ syndrome?
Problems with attention, abstraction and novelty
What is the supervisory attention system (SAS) of the frontal lobes? (Shallice)
A system in charge of the control of action and of coping with novelty, required in situations where the routine selection of actions is unsatisfactory and cognitive control or exec function is required
What is the classic executive function test task and how does it operate?
The Wisconsin card sorting task where patients are given a single card and must choose which of 4 decks to place the card on- they have to learn the rule governing which deck it should be placed on (rule could be diff colour, shape, number etc)- patient must use trial and error to find the correct rule; after 10 consecutive correct responses, rule is changed and ppt has to find the new rule again
Process often referred to as task set switching- patient must acquire a set for task performance and this can switch repeatedly during the task
What are some problems with the SAS theory of the frontal lobe?
- ‘Homolocus’ criticism aka who controls the controller
- Explains what is controlled but not how control is exercised
- Patients with frontal lesions tend to perform poorly on complex tasks and complex tasks tend to require lots of different cognitive processes
How did Miyake et al attempt to fractionate executive function into component variables using behavioural tasks and factor analysis and what did they find?
Gave healthy subjects tasks such as task switching, letter memory tasks, stop signal reaction time tasks etc
They then performed a factor analysis of all the tasks
They found that there were three v distinct latent variables accounting for performance on the 9 tasks- shifting, updating and inhibition - good model of exec functioning and tends to be used as a template for understanding how these can be fractioned
What is ‘cold’ cognition?
Broadly, functions that do NOT involve emotional or value based judgements e.g. response inhibition, task switching, error monitoring, attention and working memory
What is ‘hot’ cognition?
Broadly, functions that do involve emotional or value based judgements e.g. value based decision making, emotion guided decision making, gambling and counterfactual thinking
How did Stuss et al (2007) aim to study if there was a dysexecutive syndrome?
Tested frontal lobe patients on a range of neuropsychological tasks inc classic frontal tasks e.g. Stroop, language and memory tests requiring exec function, and attentional tests
Brain lesions mapped and location of brain damage defined by standard anatomical template
Focus on parts of the frontal lobe involved in cold cognition- dorsolateral PFC, anterior cingulate cortex
Right lateral PFC- monitoring, checking the task over, similar to’ shifting’
Left lateral PFC- task setting, ability to set a stimulus response relationship, similar to ‘updating’
Left medial PFC- energising, process of initiation and sustaining of any response
What evidence did Aron et al (2003) find there that the right inferior frontal cortex is a response inhibition ‘module’?
Aron et al 2003- demonstrated the particular importance of right inferior frontal cortex for response inhibition
Gave ppts with different brain lesions a stop signal reaction time task where they had to to respond to whether an arrow was pointing to the left or right but on occasional trials they would withold when they heard a loud beep
Found performance on this task was strongly related to the size of the lesion in the right inferior frontal gyrus
What evidence is there from fMRI studies that the right inferior cortex is a response inhibition ‘module’?
Imaging studies show increased activation in the right inferior frontal cortex during response inhibition
Healthy people in scanner are able to complete a no/go task and press a key when they see certain letters- activation in the right inferior cortex is consistently higher for no-go trials than it is for go trials, suggesting a specific role for this region
What alternative evidence is there that the fronto-parietal cortex is a multiple demand network rather than a singular module?
Duncan and Owen (2000)- meta analysis of neuroimaging studies of exec function where they plotted the activations associated with multiple diff processes e.g. response conflict, task novelty
They found that rather than separate regions of the PFC dedicated to different processes, the different processes activated similar regions- no clear separation but rather a network of regions encompassing lateral and medial PFC and the inferior parietal cortex
Duncan labelled this as the ‘multiple demand’ network, reflecting the idea that this is a multi purpose network underlying cognitive performance
What does Duncan’s ‘multiple demand’ network do?
Construction of ‘attentional episodes’, so neurons have flexible dynamic response properties and are able to encode info with the focus of attention
Adaptive coding where PFC neurons adapt their responses depending on task demands
What fMRI evidence is there from Woolgar et al that suggests the PFC performs a more complex role?
Subjects performed a task where they had to learn diff rules mapping locations to responses- when they sae a blue screen they had to remember particular mapping between locations and button presses but this was different for other colours
Used MPA to see which brain areas encoded diff info about the task e.g. rules, colours and responses
They found that although frontal and parietal regions did encode info about the position of the stimuli, the colours and responses, these regions showed strongest coding of rules
Results therefore demonstrate that the primary role of the PFC in this kind of task is encoding the information about abstract task performance e.g. rules governing stimulus response mappings- could be claimed that these regions are not simply directing attention to specific stimuli in WM but performing a more complex function
What are the key points for the role of the PFC?
PFC plays key role in organised and goal directed bhvr- structure connections and functions makes it well suited for this
Some evidence that PFC can be fractioned into diff functions but also disagreement even about what these fundemental exec functions are
Multiple demand network hypothesis offers an alternative viewpoint that there is an integrated network involved in performing cognitively demanding tasks