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.
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.
- supervised operation
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
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)
- utilisation behaviour (responding impulsively to irrelevant objects in environment)
- personality effects *eg. flat affect, apathy, disinhibition, hypersexuality)
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
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
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)
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)
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)
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)
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
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)
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
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
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
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
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
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
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.