Week 10 Lecture 10 - the executive brain Flashcards
What is executive function?
- Control processes that enable an individual to optimise performance, requiring coordination of basic cognitive
processes - Presumed necessary for ‘controlled’ behaviour in contrast to ‘automatic’ behaviour
Is executive function tied to a specific cognitive domain?
no
What can disorders of executive function result in?
difficulty with:
e.g.,
- decision making
- multi-tasking
- paying attention
- regulating emotions
- ….. etc.
What post-injury changes occurred to Phineas Gage?
- Impulsive decision making
- Impaired planning
- Poor regulation of social behaviour
What did a modern reconstruction of the damage to Phineas Gage’s skull reveal?
Damage in the left orbitofrontal/ ventromedial region and the left anterior region
What did disorders of executive function used to be called? What is executive function linked to now?
- Disorders of executive function used to be called ‘frontal lobe disorders’
- Now executive function is linked to the prefrontal cortex (PFC)
What are the 3 cortical surfaces in the PFC?
- lateral
- medial
- orbital
What are the functional specialisations in the PFC?
- refer to summary sheet for answers
How can executive function be measured in the lab?
- Task-setting and problem solving
- Overcoming potent or habitual responses
- Task switching
What are problem solving tasks (EF)?
Related to generalised measures of intelligence
What are task setting tasks (EF)?
Being presented with a goal and a starting point, then coming up with a solution
Give 2 example of task-setting and problem solving tests?
- Tower of London
- “FAS” test
What is the Tower of London task?
Beads should be moved from an initial position to a specified end-point according to the rules
What does the Tower of London task measure?
- time to complete task
- number of moves taken
A study by Shallice (1982) conducted a study using the Tower of London task.
What was the method?
- 20 healthy controls
- 61 patients with unilateral PFC lesions
CT scans used to group based on lesion
location:
- Anterior (L/R)
- Posterior (L/R)
A study by Shallice (1982) conducted a study using the Tower of London task.
What was found?
Damage to PFC results in poor performance, especially ‘left anterior’ PFC
Cognitive estimates is another example of tests of problem solving.
Give some examples of the questions that are asked in this test
- “How many camels are in Holland?”
- “How many brushings can someone get from a tube of toothpaste?”
- “How high off a trampoline could a person jump?”
What is the FAS test?
- ‘Produce as many words as you can starting with the letter F (or A or S)’
- In 1 minute
- No names
A study by Stuss et al., (1998) used the FAS test (a.k.a. letter fluency).
What was the method?
- 37 healthy controls (CTL)
- 74 patients with focal lesions in frontal and non-frontal areas
- FAS letter fluency task
A study by Stuss et al., (1998) used the FAS test (a.k.a. letter fluency).
What was found?
- Damage to the ‘left frontal dorsolateral
cortex’ (LDL) particularly decreases
performance - Fewer words in total vs. CTL (control group)
What is a habitual response?
- A habitual response is one that we engage in automatically
- This aspect of executive function is related to the concept of inhibition
- Reducing the likelihood of a particular thought or action
Give 2 examples of tests that measure overcoming habitual responses (EF)?
- Stroop test
- go/no go test
What is the suggested explanation for the difficulty of the Stroop test?
- Reading the word is automatic, so generates an incorrect response
which must be inhibited - Incorrect response competes with the less-automatic task of naming the ink colour
A study by Alexander et al., (2007) used the Stroop test to investigate neural correlates with EF.
What was the method?
- 38 healthy controls
- 42 patients with frontal lesions
- Stroop task (modified)
fMRI to relate lesion location to:
* Reaction times
* False positive – responding to Distractors/ Other with Button 1
* False negative – responding to Targets with Button 2
A study by Alexander et al., (2007) used the Stroop test to investigate neural correlates with EF.
What was found?
- Lesions in left ventrolateral PFC = more false positives to Distractors
- Lesions in a right superior medial region (anterior cingulate, pre-supplementary motor area, and dorsolateral areas) = slow reaction time and decreased correct responses
What is the go/ no go test?
- Make a response (‘Go’) for certain stimuli but inhibit (‘No-go’) for other stimuli
- In the experiment, more trials with ‘Go’
stimuli ‘No-go’ - Start to respond habitually to stimuli
with ‘Go’ response
Picton et al., (2007) used the go/ no go test to study EF.
What was the method?
- 38 healthy controls
- 43 patients with focal frontal lesions
- Grouped using MRI or CT scans
Go/No-go paradigm:
* Letters A, B, C, D all with equal probability
- Stage 1 – “improbable go”:
- Go: A
- No-go: B, C, D
- Stage 2 – “improbable no-go”:
- Go: B, C, D
- No-go: A subjects must inhibit “an infrequent, prepotent response”
[habitual – typical no-go condition] - Reaction times
Errors - - Misses
- False alarms – related to impulsivity
Picton et al., (2007) used the go/ no go test to study EF.
What was found in terms of reaction times?
- All subjects slower after making a false
alarm in Stage 2 - SM group: lesions in superior medial frontal lobe were slowest of all
Variability of reaction times:
* More variable in group with lesions in
ventrolateral PFC, possibly reflecting
impaired monitoring of performance
Picton et al., (2007) used the go/ no go test to study EF.
What was found in terms of errors: false alarms?
SM group: lesions in superior medial frontal lobe associated with more false alarms
* Dorsomedial PFC
* Anterior cingulate cortex (ACC)
* Pre-supplementary motor area (pre-SMA)
What is an evaluative point for task-setting and problem solving tasks (EF)?
Accuracy of lesion identification with CT scans?
What are 2 evaluative points for tests concerning overcoming habitual response (EF)?
- Not all models of executive function rely on the concept of ‘inhibition’ but instead consider biasing activation signals
- Maybe a bias towards the ‘correct answer’ (ink colour) is needed, rather than an inhibition of the ‘incorrect answer’ (colour name)
What is task switching? (EF)
Related to the concept of perseveration: failure to shift away from a previous response
Give an example of task switching?
Wisconsin Card sorting test
What is the Wisconsin Card Sorting Test?
Match a card to 1 of 4 reference cards
Symbols on cards vary in:
* Shape
* Number
* Colour
* But subjects not specifically told this!
What do reaction times in the Wisconsin Card Sorting Test tell us?
- A: minimal change in RT between No-switch and No-switch trials
- B: Big difference in reaction times between No-switch and Switch trials
- The Switch Cost
What is the switch cost?
a slowing of response time due to
discarding a previous schema and setting up a new one
Meuter & Allport (1999) conducted a study investigating the switch cost.
What was the method?
- 16 Bilinguals
- Numeral naming from text
Measured difference in reaction times when switching:
* 1st (dominant) to 2nd (weaker) language
* 2nd to 1st language
Meuter & Allport (1999) conducted a study investigating the switch cost.
What was found?
- Bilinguals are slower at switching from 2nd language (hard task) to 1st language (easy task)
- The Switch Cost is greater because inhibiting the more complex schema has a cost
Shallice et al., (2008) looked at the neural correlates for task-switching.
Who were the participants, what lesions were involved?
*38 healthy controls
41 patients with focal PFC lesions:
* Left lateral (LL)
* Right lateral (RL)
* Inferior medial (IM)
* Superior medial (SM)
Shallice et al., (2008) looked at the neural correlates for task-switching.
What was being measured?
Task switching effects on RT and errors:
* Trial type (Switch/Repeat)
* Congruent/Incongruent button press
* Delay of cue (e.g., “Left or Right?”) on the screen long before or not long before
trial
Shallice et al., (2008) looked at the neural correlates for task-switching.
What was found?
- Reaction times slowest for SM group
- Greater Switch Cost than controls
- Error rates highest IM group
Linked to lesions in:
* Ventral orbitofrontal cortex
* Medial and orbitofrontal PFC
What is the Supervisory Attentional
System?
A model consisting of a set of tasks and behaviours (schemas) and a biasing mechanism to activate/inhibit these according to current goals
What does the supervisory attentional system look like?
look at summary sheet for answers
Evaluation: tests of executive function:
What is evidence from lesion studies highly dependent on?
- The nature of the task (and any modifications)
- How patients with lesions are grouped
Evaluation: tests of executive function:
Real-world evidence?
- Sometimes, individuals with damage to PFC can pass standard laboratory tests despite exhibiting impairments in real-world behaviour
- How much is the Wisconsin Card Sorting Test really like task-switching in the real world?
Evaluation: tests of executive function:
How are the tests developed?
Tests developed coincidentally as we learned more about neural correlates of executive function?
Give 3 examples of contrasting areas involved in EF.
- Orbital/ventromedial vs. lateral PFC
- Posterior vs. anterior lateral PFC
- Anterior cingulate cortex (ACC) vs. lateral PFC
What are Hot vs. Cold control processes?
Control processes differ based on the nature of the stimuli being processed
- ‘Hot’ stimuli – affective or reward-related
- E.g. food (non-human animals) or money (humans)
- ‘Cold’ stimuli – purely cognitive
- E.g. sensory dimensions such as shape, colour
What are the different neural correlates in the PFC for Hot vs. Cold control processes?
- ‘Hot’ stimuli – orbitofrontal cortex
- Which has connections with posterior affective areas
- ‘Cold’ stimuli – lateral frontal cortex
- Which has connections with posterior sensory/motor areas
In terms of Orbitofrontal/ventromedial PFC vs. lateral PFC:
What is reversal learning?
- Learning that a previously rewarded stimulus or response is no longer rewarded
- ‘Hot’ control process
In terms of Orbitofrontal/ventromedial PFC vs. lateral PFC:
What is set shifting (a.k.a task-switching)?
- Discarding a previous schema and establishing a new one
- ‘Cold’ control process
In terms of Orbitofrontal/ventromedial PFC vs. lateral PFC:
Dias et al. (1996) conducted a study on marmoset monkeys.
What was the procedure?
- Compound stimuli made of lines and
shapes - Training to respond to certain items in a
dimension (e.g., a circle Shape) through
reward until learned, regardless of the
other dimension (any Lines)
Lesions in either:
* Orbitofrontal cortex
* Lateral frontal cortex
Post-lesion training:
* Reversal: same Shapes and Lines, but
rewarded for different Shape (unlearn
old rule)
* Dimension shift: new Shapes, rewarded
for a certain Line (learn a new rule)
In terms of Orbitofrontal/ventromedial PFC vs. lateral PFC:
Dias et al. (1996) conducted a study on marmoset monkeys.
What was found?
- a double dissociation (see summary sheet)
- Suggests dissociable neural correlates for control of reward-related (‘Hot’) vs. purely cognitive (‘Cold’) stimuli
For individuals with PFC lesion, what could a distinction between brain areas responsible for ‘Hot’ and ‘Cold’ control processes explain? What did this lead to?
could explain individuals with PFC lesions who are:
* Impaired in the real-word (e.g., impaired regulation of social behaviour)
* ‘Hot’ – salient rewards for appropriate social interactions (e.g., in-group benefits)
* Spared in laboratory tests of executive function
* ‘Cold’ – cognitive dimensions such as shape/colour without salient rewards
* (unless money…?)
lead to development of the somatic marker hypothesis
What is the Somatic Marker Hypothesis (Damasio, 1996)?
Proposes that emotional and bodily states
associated with previous behaviours are used to influence decision making
- Emotional events (e.g., a risky situation) store ‘somatic markers’ in memory
- Somatic markers are believed to be stored in orbitofrontal/ventromedial PFC
- Somatic markers may be unconscious or conscious
- Retrieving that event reinstates the somatic marker (if PFC undamaged…)
- This guides behaviour (e.g., making a response more or less likely)
What evidence is there for the Somatic Marker Hypothesis?
Iowa Gambling task
What is the Iowa Gambling task?
Iowa Gambling task
* Subjects given a “loan” of $2000
* Each round, choose a card from 1 of 4 decks
* Receive either a gain or a penalty
Decks have different returns over the entire test:
* A+B = ‘Bad’ decks
* C+D = ‘Good’ decks
What are the results from the Iowa Gambling task for healthy controls?
- Learn to switch from ‘Bad’ decks (A+B) to ‘Good’ decks (C+D)
- Show anticipatory skin conductance response when selecting from ‘risky’ (‘Bad’)
decks during the game
What are the results from the Iowa Gambling task for Patients with orbitofrontal PFC lesions?
- Fail to switch from ‘Bad’ decks to ‘Good’ decks
- Do not show anticipatory skin conductance response when selecting from ‘risky’ decks
- Show intact performance on other tests of executive function (Stroop, WCST)
Patients with orbitofrontal PFC lesions fail to switch from ‘Bad’ decks to ‘Good’ decks in the Iowa Gambling task.
Explain how this could be a failure of reversal learning
- Early in the game: Decks A+B are rewarded
- Because Decks C+D have smaller gains
- Late in the game: Decks C+D
are rewarded - When early-game gains are equivalent for ‘Bad’ and ‘Good’ decks, patients with
ventromedial PFC perform as controls (Maia & McClelland, 2004)
What does the posterior PFC include?
premotor cortex, and regions such as
Broca’s area
Is the anterior PFC understood?
less well-understood until recently
What is the anterior PFC though to be involved in?
Multi-tasking:
- Carrying out several tasks in succession
- Requiring both task-switching and maintaining future goals in mind,
while dealing with current goals - These tasks in isolation do not recruit anterior PFC
- Combined, the PFC is implicated
Koechlin & Summerfield (2007) proposed a hierarchically ordered executive system.
What did this look like?
anterior→posterior gradient for simple→complex tasks
Koechlin & Summerfield (2007) proposed a hierarchically ordered executive system.
Explain the hierarchy in detail
Sensory control:
* Premotor cortex
* Simple stimulus-response mappings
- Contextual control:
- Posterior lateral PFC
- Learned contextual information (rule set)
guides response - Branching control:
- Anterior lateral PFC
- Using episodic control to switch to a different context (rule set)
- Branching control:
- Polar lateral PFC
- Maintaining current episodic control and a pending context (other task goals - complex multi-tasking)
(also see summary sheet)
What are the subdivisions of the Anterior Cingulate cortex (ACC)?
- Dorsal region implicated in executive functions
- Ventral region implicated in emotional
processing
Humans and non-human primates are slower and more accurate after making an error
What evidence is there to suggest that this process recruits the ACC?
- ACC lesions in monkeys → Error +1 is not slower or more accurate
- EEG evidence of a response in the ACC to errors
What is error related negativity?
an event-related potential component in EEG detected when an error is made
Where does error related negativity appear to have its origin?
in the ACC
van Veen & Carter (2002) investigated the role of the ACC in terms on response conflict.
What was the method?
Stroop with modification about response conflict expectancy
Trial types:
* Congruence expected – low involvement of strategic processes
* C/c = congruent trials
* C/i = incongruent trials
- Incongruence expected – high involvement of strategic processes
- I/c = congruent trials
- I/i = incongruent trials
van Veen & Carter (2002) investigated the role of the ACC in terms on response conflict.
What was the result?
ACC activation when trials are unexpectedly incongruent, i.e.,
involving most response conflict
What can Orbital/ventromedial vs. lateral PFC also be known as?
emotional vs. cognitive control
What can Posterior vs. anterior lateral PFC also be known as?
simple vs. complex/multiple tasks
What can ACC vs. lateral PFC also ben known as?
error detection vs. control of responses
