W10.1 (C): Orbitofrontal cortex, the striatum and dopamine Flashcards
(24 cards)
What is the IOWA gambling task and what did it aim to measure?
Role of the orbitofrontal cortex in cognitive control
Ppts (normal controls and those with lesions) were given 4 decks and were asked to choose one to get a reward or punishment- over time, they learnt which decks were risky and which were safe- good decks led to wins over the long run whereas bad decks led to losses. Galvanic skin responses were also studied along with behavioural data
What BEHAVIOURAL results were found in the IOWA gambling task?
Normal controls learnt over time that they were losing money and learnt to select the good decks. Patients with other lesions showed similar responses whereas patients with specific OFC lesions did NOT learn to select good responses
What SKIN CONDUCTANCE results were found in the IOWA gambling task?
There was not much difference between reward and punishment phase in the amount of sweating, but there was a difference for the anticipatory phase (where ppt makes the decision and waits to see if they won); this differed across controls and OFC patients.
What does the OFC support the learning of according to the IOWA gambling task results?
Supports the learning of associations between somatic markers and complex situations- the OFC can then use this info to assess likely outcomes of behavioural choices
What are some issues with the Iowa Gambling task?
Cards are presented in a fixed order that induces a preference for the risk decks (wins are experienced early, losses experienced later); in order to perform well on this task, subjects must at some point overcome this preference and switch to choosing the ‘good’ decks
What is the process of inhibition and stitching known as?
Reversal learning- based on value of our choice where we measure up a judgement
What is the somatic marker hypothesis? (Damasio)
Hypothesis that says emotional information in the form of physiological arousal is needed to guide decision making
Somatic markers are the bodily responses to emotional stimuli- these are used to guide decision making
What was done differently in the study variation in the second Iowa Gambling task and what did they find?
The order of cards was changed- they had the standard version where the risky deck losses were experienced later (reversal learning required) and a variant of the IGT (risky losses experienced early so no reversal learning)
Impairment disappears in variant of the IGT in which risky losses are experienced earlier and therefore reversal learning is not required, suggesting a deficit in reversal learning rather than a value based decision more broadly- does not seem to be such an impairment when no reversal learning is required
What are some problems with reversal learning hypothesis of OFC function in monkey studies?
Monkeys with OFC lesions do not always show a reversal learning deficit
In one study, monkeys had to select either a small or large reward- if they selected the small reward, they were given the large one and vice versa- monkeys with OFC lesions are actually learning the task and performing task just as well as those without, so the idea that the OFC is involved with unlearning of rewards does not fit in with this data as monkeys with lesions perform well and are able to learn not to select the large reward initially
Why is it the case that monkeys with OFC lesions are able to learn and perform in tasks just as well as those without lesions?
Task in this study involves overcoming a strong innate preference for larger food rewards which is quite different for standard tasks that involve learning and suppression of arbitrary stimulus-outcome relationships
Rate of learning is much slower for learning whereas reversal learning takes place over a shorter pace of time
What does evidence into monkey lesions suggest about the OFC and reversal learning?
Suggests OFC may only be required for reversal learning when the stimulus outcome computations are made and suppression involves arbitrary stimulus outcome relationships. The adapted coding idea of the PFC where neurons are rapidly reconfiguring as the task evolves and we code whatever is task relevant
What do recent perspectives on OFC function emphasise?
Emphasise the computation of value- the OFC converts outcomes into a common neural currency on which to base choices which may account for the role OFC seems to play in complex emotions such as regret
How did Camille et al (2004) investigate the role of the OFC in the generation of regret?
Ppts chose one of two wheels with different chances of winning- they either got partial feedback where they found out what they won and also knew the possibilities of what they would’ve won if they chose the other wheel but did not get to know the amount, OR they got the full feedback. Ppts were asked to rate how satisfied they were with their outcome. Normal subjects had higher levels of satisfaction when they won but also when they found out they wouldve lost more on the other wheel if they had lost much lower satisfaction if they found out they would’ve won more or lost less on alternative wheel. OFC patients did not show this pattern of thinking and did not modulate their ratings according to whether the alternative wheel would’ve been a win or loss- suggests that the key role of the OFC is being able to experience the consequences of winning and losing but more importantly to integrate info from diff sources of outcome
Summarise the role of the OFC in decision making
- Facilitating effective decision making based on the knowledge of the value of different actions
- Suppressing actions based on recently learned action-outcome relationships
- OFC seems necessary for value computations only when based on new info
- Ability to mentally stimulate info about predicted outcome is key
What is the striatum/basal ganglia and what is its role?
A subcortical region in the brain that has traditionally been associated with motor function and more recently, exec function. Striatum is one of the most strongly connected regions to the PFC- loops seem to occur in parallel with diff loops connecting different pFC regions and hypothesised to play different roles e.g. such as reward processing
What are the two main types of dopamine receptors and where are they produced?
Produced by dopaminergic neurons in VTA- several diff types of DA receptors (D1 to D5)- broadly categorised as D1 and D2 types
D1- more abundant in PFC
D2- more abundant in striatum
What are the four main pathways dopamine travels through?
Mesolimbic
Nigostriatal
Mesocortical
Tuberoinfundibular
What is the role of dopamine (DA) in addiction?
Modern theories emphasise learning and motivation effects of dopamine over pleasure
Drugs enhance DA function by acting on midbrain neurons to increase extracellular concentrations of DA
DA neurons in the striatum encode reward prediction error (discrepancy between expected and gained reward)
Prediction errors play a key role in the development of addiction
How does dopamine influence cognitive control?
One theory suggests it plays diff roles depending on site of action where D1 receptors are linked to stability of representations and D2 receptors are linked to facilitating flexible behaviour
Dopamine may achieve a balance of stability and flexibility by exerting diff effects on striatal and PFC activation
What is the role of dopamine in working memory and exec function?
Dopamine depletion in PFC of monkeys causes a deficit in spatial WM that is nearly as severe as completely removing PFC
Evidence from Parkinson’s disease- supports idea that striatum may be implicated in exec function such as planninh
How were the effects of drugs (Ritalin) on brain activation displayed in a study involving reversal learning and what did results find? (Dodds)
Examined the effects of a medication commonly used to treat ADHD (dopamine reuptake inhibitor leading to an overall increase) on brain activation during reversal learning
Healthy ppts given a probabilistic reversal learning task in MRI
On each trial, ppts were presented with two abstract visual patterns- they had to discover which of these was correct- feedback given a green or red smiley face if they had got it right or not. After correct trials, contingencies switch and the subject must switch to selecting the other pattern
Results showed that part of the striatum was the only region to show such modulation to the task
What do the results of Dodds et al imply about the role of dopamine and the striatum?
That striatal dopamine has a clear role in mediating cognitive flexibility
What evidence is there for the dual role of dopamine in maintaining the stability of the responding PFC and switching striatum? What did they find?
Dopaminergic signalling in the striatum could account for individual differences in traits e.g. impulsivity that are risk factors for ADHD
Cools et al examined the effect of a D2 receptor antagonist on switching behaviour and neural activation in the striatum- the colour of fixation cross instructed subjects to encode faces or scenes- trials were either switch or nonswitch
Found that high impulsives had a big switch cost compared to low impulsives- the drug tended to mediate this effect which suggests it is able to reduce switch costs only in those who are high impulsive
Summarise the role of the striatum and dopamine in executive function?
Striatum plays a key role in exec function- deep part of the brain that seems to be very involved in the PFC which when left to its own devices would probably not switch
Parkinsons disease provides evidence for this and involves a deficit in cognitive flexibility suggesting a role for striatal dopamine
Effects of dopamine on exec function may depend on the site of action- striatum with cog flexibility and PFC cog stability
