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What are 2 sets of distinctions we need to make when talking about the function of executive functions?
- Automatic vs Controlled behaviour (Shiffrin)
- eg. driving car can often be automatic, but when unexpected happens, behaviour overriden by cognitive control to deal with novel situation
- Top-down
vs Bottom-up control (Desimone & Duncan) - eg. stopping car for shopping is top-down and goal-driven; stopping car for red light is bottom-up and stimulus-driven.
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Executive functions are processes that __ behaviour with a view to __ performance. They are considered to be particularly useful in situations that require the __ __ of a number of cognitive processes.
- control
- optimise
- supervised operation
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Norman & Shallice outlined 5 types of situations in which top-down executive control processes would be more beneficial than automatic activation of behaviour. What are they?
- 1. planning or decisions making
- 2. error correction or trouble-shooting
- 3. responses contain novel sequences of actions
- 4. involve technical difficulty or danger
- 5. require overcoming of strong habitual responses
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Patients with lesions in prefrontal cortex tend to have particular difficulty in undertaking those 5 types of actions. Common behavioural symptoms of dysexecutive/frontal lobe syndrome include?
- perseveration (repetition)
- distractibility
- utilisation behaviour (responding impulsively to irrelevant objects in environment)
- personality effects *eg. flat affect, apathy, disinhibition, hypersexuality)
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Give 2 clinical tests of executive function (esp about planning in an organised and coordinated way).
- Tower of London task (Shallice 1982)
- Measure ability to plan steps needed to move beads from an initial position to a specified end point
- Multiple Errands test (Shallice & Burgess)
- Participants mulit-task in real-life high street, trying to optimise performance in taking the fastest route etc
- Results on both: frontal lobe injury - often fail to plan in organised or coodinated way
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Does do results of these two clinical tests correlate with neuroimaging evidence?
- Rowe et al (2001)
- activation in left dorsolateral prefrontal cortex during performance of Tower of London task
- Thos with damage to frontal lobe require significantly more moves, tending to perform by trial and error
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What parts of executive functioning does Wisconsin Card Sorting Test assess? What does it involve?
- Milner 1963
- Assesses: overcoming strong habitual response, error correction, trouble-shooting
- Method: Must sort cards accordingt o one of number of rules (shape, colour etc) that can change unexpectedly requiring shifting of responses to new rule on basis of feedback that the previous response was incorrect.
- Frontal lobe lesion: typically fail to shift when given feedback, continue habitually responding according to previous rule (they perseverate)
- Neuroimaging: monitoring feedback on this task associated with activation in dorsolateral PFC (Monchi et al)
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What is another test that assesses the ability to inhibit habitual behaviour?
- Stroop test
- Based on principle that reading words is more habitual than identifying colours
- Left PFC lesions: difficulty inhibiting word reading (Perret, 1974)
- Neuroimaging: activation in frontal areas like anterior cingulate during task (Bench et al)
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What is the evidence for linking frontal lobe regions to ability to undertake tasks that are technically difficult.
- Often dual-task interference tests (performing two tasks concurrently)
- Patients with frontal lobe lesions impaired during dual-task conditions (look at previous lectures)
- Healthy volunteers exhibit activation in dorsolateral PFC (D'Esposito et al, 1995)
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What brain region is associated with the assessment of danger and risk? What case study?
- Damasio suggested ventromedial PFC important
- esp as it involves use of emotional, reward-based information
- Phineas Gage: lesions to this area often associated with inability to assess risk appropriately
- (ALSO have affect on personality - making people more antisocial)
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So, just to sum up these clinical tests/evidence for testing executive functions - what are the broad areas we've looked at?
- 1. Planning: Tower of London, Multiple Errands
- 2. Inhibiting habitual/automatic response (and shifting behaviour): Wisconsin Card Sorting test, Stroop test
- 3. Technical difficulty: dual-task intereference (look at previous lectures + D'Esposito fMRI)
- 4. Assessment of danger/personality: case studies like Phineas Gage (others?) and Damasio
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So, frontal lobes seem very important. Tell me a bit about how human frontal lobes are unique and why we think it's important for coodinating wide range of processes in brain.
- Frontal lobes disproportionately larger in humans than in orhter species, occupying almost 1/3 of cortical volume (Fuster, 1989)
- Evolutionary enlargement matched by greatly increased frontal connectivity in humans (Schoenemann et al)
- Frontal lobes have extensive conenctions with other cortical systems involved in perception, memory, emotion etc, as well as between frontal sub-regions (suggesting it is important for coordination of wide range of processes)
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Explain what the Supervisory Attentional System model is and who first proposed it.
- Norman & Shallice (1986)
- Controlled behaviour arises through selection/implementation of schemas (action routines)
- Schema selection can be triggered in 2 ways:
- 1. contention scheduling (bottom-up triggering in routine situations)
- 2. use of supervisory attentional system (additional top-down control in non-routine situations)
- So... it's a system that provides additional top-down control when selecting schemas (action routes) esp in non-routine situations
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How does the Supervisory attentional system model (SAS) explain the performance of patients with frontal lesions on tests of executive function?
- Stroop task: once activated, dominant schema 'read word' persists in absence of inhibition by SAS (perserveration)
- Multiple Errands: disruption to selection and appropriate sequencing of schema by SAS leads to disorganised behaviour.
- Distractibility: task-unrelated schemas capture attention
- Utilisation: sensory info capturing attention and, in absence of SAS inibition, leading to uncontrolled behavioural responses
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When the model was first proposed by Norman & Shallice (1986), they assumed single executive function system (the SAS) supported by frontal lobes. However, what evidence suggests this might not be the case? (4)
- Some patients fail some executive tasks, but perform well on others
- Often poor correlations between performance on different executive tasks
- Factor analysis on performance on different tests typically yields multiple separable factors
- fMRI indicate distinct frontal regions may play different roles in executive tasks
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On that basis, who revised the SAS model? How was it revised?
- Shallice & Burgess (1996)
- Schema can be specified in 3 ways:
- 1. spontaneously (by stimuli in environment or goals)
- 2. as outcome of problem solving
- 3. triggered by prior intentions
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According to this revised model, what is the process after a schema is selected?
- maintained in working memory
- implemented through effector systems as behavioural action plan
- after implementation, results (behavioural outcomes) assessed against pre-specified goal criteria
- decision made whether to continue with schema or reject it or generate new one with revised specifications
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What is not consistent about this model with neuroimaging evidence?
Neuroimaging suggest novel and routine behaviours both activate reiongs of PFC, which is not obviously consistent with model
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Outline some other prominent models of executive functions (not examined but good to know).
- Somatic marker hypothesis (Damasio): decisions about emotional events (eg. risky situation) guided by somatic markers which link previous memory with physiological state induced by them
- Adapive coding model (Duncan): common 'global workspace' in frontal lobes. Neurons flexibly code task-specific info and can adapt to perform many different cognitive operaions, rather than there being multiple executive processes.
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