Week 8 - Executive Brian Flashcards
1
Q
What are executive functions?
A
- Executive functions - the complex processes by which an individual optimizes his or her performance in a situation that requires the operation of a number of cognitive processes (Braddeley, 1986)
- Executive functions are not tied to one particular domain (memory, language, perception, etc.).
- Specific examples:
- Attentional control
- Inhibitory control
- Problem solving
- Working memory (e.g., mental simulation)
- Executive functions are needed to optimise performance when a situation is novel and/or difficult (when several cognitive processes need to be coordinated)
- Executive functions regulate cognitive (e.g., driving a car) and social/emotional (e.g. making a good impression) outcomes
- Executive functions are associated with the prefrontal cortex
2
Q
What are the six tasks that are designed to study executive functions?
A
- Tower of london task
- FAS test
- Stroop test
- Eriksen flanker test
- Go/No-go test
- Wisconsin card sorting test
3
Q
What is the tower of london task? (Shallice, 1982)
A
- Planning/Problem solving
- Getting from a start to an end
- Damage to left PFC results in poor performance (Shallice, 1982):
- PFC patients takes significantly more moves –> they perform the task by trial and error rather than planning their moves
- fMRI study with healthy participants:
- Dorsolateral Prefrontal Cortex (DLPFC) is activated during the task
- Strength of the activity depended on task difficulty
4
Q
What is the FAS test? (Miller, 1984)
A
- Generate a sequence of words beginning with a specific letter (“F,” “A” or “S”) in 1 min
- E.g. substantial, sum, subtraction
- A measure of verbal fluency
- Patients with left lateral prefrontal lesions are particularly impaired (Stuss et al. 1998)
- Tombaugh et al (1999) tested patients on the FAS test:
- Conducted in Canada (n=1300)
- Average total number of words generated in 1 minute for the letters F, A, and S
- Educational level correlated with performance
5
Q
What is the stroop test? (Stroop, 1935)
A
- Measure the ability to overcome a habitual response (i.e., inhibitory control)
- Participants are asked to name the colour of the ink (and ignore reading the word) as quickly as they can
- People make more errors and take longer to respond in the incongruent condition
6
Q
What is the Eriksen flanker test? (Eriksen & Eriksen, 1974)
A
- Measure the ability to overcome a habitual response (i.e., inhibitory control)
- Participants are asked to judge the direction of the central arrow (left or right) as quickly as they can
7
Q
What is the Go/No-Go test?
A
- Measure the ability to overcome a habitual response (i.e., inhibitory control)
- Participants are asked to respond to a frequent stimulus (go trials) but withhold a response to another stimulus (no-go trials) – press a key when you see green
- Measure of impulsivity (proportion of errors on no-go trials)
8
Q
What is the evidence for the Stroop, Flanker and Go/No-go tests?
A
- dorsal Anterior Cingulate Cortex (dACC) is activated in these tasks.
- Pre-supplementary Motor Area (Pre-SMA) is also activated.
- Stroop and Flanker tests - Incongruent > Congruent conditions – causes activation
- Go/No-go test - No-go > Go conditions – causes activation
- Dorsolateral prefrontal cortex (DLPFC) is also implicated in these tasks
9
Q
What is the Wisconsin Card Sorting Test? (Milner, 1963)
A
- A test of executive functions involving rule induction and rule use
- Classify cards according to different criteria
- 3 possible criteria; 1) colour, 2) number, and 3) shape
- Receive feedback (correct or incorrect) after each trial
- The classification rule changes every ~10 cards (trials)
- The task measures how well people can adapt to the changing rules (i.e., task-switching).
- Many patients with damage to prefrontal cortex fail to make rule shift and continue to incorrectly sort according to the previous rule (known as perseveration)
- Rushworth et al., (2002):
- fMRI: Medial frontal lobes (pre-SMA) are associated with reassignment of stimulus-response parings
- TMS: TMS to pre-SMA disrupted task-switching –> pre-SMA is essential for task switching
10
Q
What is the summary of executive functions and the brain?
A
- Tasks that assess executive functions are associated with prefrontal cortex
- Tower of London (planning/mental simulation) -> DLPFC
- FAS test -> left LPFC
- Stroop test, Flanker test (response conflict) & Go/No-go test (inhibition) -> pre-SMA, dACC (dorsal Anterior Cingulate Cortex) & DLPFC
- Wisconsin Card Sorting task (task switch) -> pre-SMA (supplementary motor area)
11
Q
What is the organisation of executive functions?
A
- Orbital/ventromedial vs. lateral PFC – Emotional (hot) vs. cognitive (cold) control
- Posterior vs. anterior lateral PFC – Simple vs. complex control
12
Q
What are hot and cold control processes?
A
- Control of affective or reward-related stimuli are hot processes
- Control of purely cognitive stimuli are cold processes
- An important principle of organisation of executive functions
13
Q
What is the initial evidence from Dias et al.’s (1996) study with marmosets that there are two different processes - hot and cold
A
Initial Training Phase:
- Simple discrimination task where certain stimuli were consistently rewarded – presented with a pair of stimuli that the monkey has to pick one of them.
- In this example, lines are irrelevant (uncorrelated with reward) – shapes are relevant
Neurochemical lesions:
- Parts of monkey’s brain was destroyed by neurotoxic
- Three experimental groups:
- Lateral prefrontal cortex (LPFC) lesion group
- Orbitofrontal cortex (OFC) lesion group
- Control (no lesion) group
Post-surgery Testing Phase:
- Monkeys in all three groups performed this task well
- Abilities to discriminate different stimuli and learn new associations are intact
- Second task is an extra-dimensional shift – shapes are no longer relevant, lines are relevant instead.
- LPFC group took significantly longer to learn
- Damage to LPFC causes a loss of inhibitory control in attentional selection (stimulus related inhibition; e.g., they cannot ignore shapes)
- Third task – stimuli associated with reward switch
- OFC group took significantly longer to learn after reversal
- Damage to OFC causes a loss of inhibitory control in affective processing (reward related inhibition; e.g., they cannot stop picking previously-rewarded shapes)
- LPFC group cannot ignore shapes (loss of stimulus related inhibition)
- OFC group cannot stop picking previously rewarded shapes (loss of reward related inhibition)
Summary:
- Dias et al.’s (1996) finding is evidence for two separate inhibitory control processes, which are localised in two different brain regions (OFC/vmPFC vs. LPFC); one reward-related (“hot”) and another related to stimulus dimensions (“cold”)
- This finding provided an important insight into a puzzle from older literature
- Some patients with PFC (vmPFC) damage could pass standard (“cold”) tests of executive functions, but tend to make bad financial (and social) decision
14
Q
Who was Phineas Gage?
A
- Phineas Gage was a “responsible, intelligent, well socially adapted” construction worker.
- In 1848, a work accident resulted in an iron bar going through his face, skull and brain.
- Following the accident, Gage’s personality changed dramatically:
- He was no longer responsible, which resulted in the loss of his job.
- He did not comply to social norms.
- His behaviour became impulsive and disrespectful.
- Ability to learn or decide based on reward/punishment is impaired? - hot and cold processes
15
Q
What is the Somatic Marker Hypothesis? (Damasio)
A
- Somatic Marker Hypothesis - people experience bodily, visceral feelings (“gut feeling” or somatic marker) that guide their decisions based on the anticipated pain or pleasure of the outcomes.
- Emotion important for optimal decision making
- Somatic Marker Hypothesis was created to attempt to account for the mechanism underlying the deficits in everyday functioning experienced by patients with ventromedial prefrontal cortex (vmPFC) (and OFC) damage
16
Q
How does Temporal Discounting (delay discounting) provide further evidence supporting the functional distinction between vmPFC (“hot”) and LPFC (“cold”)?
A
McClure et al. (2004) conducted an fMRI study using the temporal discounting task:
- Two distinct neural processes (dual-system model):
- Fast, automatic, and context-dependent (e.g., emotion-based decision; “hot”)
- Slower, controlled, and evidence-based (e.g., decision based on deliberation; “cold”)
- PCC, mPFC and Ventral Striatum activated when making SS (smaller-sooner) rewards.
- RPar, DLPFC and LOFC activated when making slower-evidenced based decisions.
Summary:
- Hot vs. cold processes:
- Executive functions are domain general, regulatory processes
- Lateral PFC regions are associated with “pure” cognitive regulation (“cold”)
- Orbital/ventromedial regions are associated with emotional cognitive regulation (“hot”). This may be a result of somatic markers stored in the vmPFC and OFC region OFC LPFC
- Damage to either region can therefore differentially affect behaviour
17
Q
What are the different types of control involved in anterior and posterior LPFC?
A
Koechlin & Summerfield (2007) proposed a model about processes involved in anterior and posterior LPFC:
- Believed anterior LPFC is responsible for more complex control, whereas posterior LPFC is for simple control.
- There are four different types of control:
- Sensory control - simple stimulus response mapping:
- A telephone ringing -> lift it from the receiver
- Behaviour depends only on stimulus
- Contextual control - control signals related to an immediate context in which a stimulus occurs:
- The phone rings when you are visiting your friend
- Whether or not you answer the phone depends on the context
- Behaviour depends on stimulus and context
- Episodic control - control signals related to past events:
- You are at a friend’s house, but your friend is busy, your friend asks you to answer the telephone if it rings
- Behaviour depends on stimulus, context, and episode (i.e., instruction)
- Branching control - pending tasks while carrying out an ongoing task (i.e., multitasking):
- You are at a friend’s house, but your friend is busy, your friend asks you to answer the telephone if it rings. However, your friend tells you that he will soon be expecting an important call and wants to answer it himself.
- Behaviour depends on condition (e.g., Until A, do B, then do C), episode, context and stimulus
18
Q
What did Koechlin et al. (2003) show about the different types of control?
A
Koechlin et al. (2003) experiment looking at the different types of control:
- Sensory control manipulation:
- Green = response 1 (e.g., press right key)
- Red = press response 2 (e.g., press left key)
- Contextual control manipulation:
- Perform consonant/vowel discrimination for red letters and Upper/lower case discrimination for green letter
- Episodic control manipulation:
- Stimulus-response mappings stay the same across blocks (left) vs. change in each block (right)
- Results:
19
Q
Outline Koechlin et al’s 1999 study
A
Koechlin et al. (1999):
- Stimuli - sequences of upper- or lower-case letters from the word `tablet’.
- Control condition - decide whether two successively presented letters were also in immediate succession in the word `tablet’
- Delay condition - do the same task, while ignoring lower-case letters
- Dual task condition - subjects had to respond as in the control condition for both upper- and lowercase letter series with one exception. Subjects had to decide whether every first letter indicating a case change was the letter T (or t).
- Branching condition - subjects had to respond to upper-case letters exactly as in the delay condition and to lower-case letters exactly as in the dual-task condition.
- Results:
- Yellow = main effect of dual task
- Green = main effects of both delay and dual task
- Red = interaction between delay and dual task (i.e., branching control)
- Anterior part of LPFC correlated with highest activity for branching
20
Q
What are the roles of the Anterior Cingulate Cortex?
A
- Executive functions accounts for 19% of tasks used to measure Anterior Cingulate Cortex.
Brown and Morey (2012) - dACC is related to:
- Inhibition – found by using the Go/No-go test
- Comparing no-go > go – we see activation in the dACC.
- When you see a red stimulus, you have to inhibit your response.
- Response conflict - simultaneous activation of incompatible response tendencies:
- Found by using the Stroop test/Eriksen Flanker test
- Comparing congruent condition to incongruent conditions – we see activation in the dACC.
- Decision conflict - conflict that occurs when people feel uncertain as to which option to choose from a set of similarly attractive (or unattractive) options:
- Pochon et al. (2008) asked people to say which face is more attractive – if the faces were similar, activation occurred in the dACC.
- Error processing:
- Whenever we make errors, we observe EEG signal of ERN.
- ERN is event-related potential generated by the ACC which peaks roughly 100 ms following errors on many speeded reaction time (RT) tasks
Furthermore…
- dACC is activated by reward and punishment (e.g., monetary gain and loss, respectively), especially when they are unexpected –> role of dACC plays an important role in learning
