OFC Stiratum (10b) Flashcards
(17 cards)
Original Evidence: What is the Iowa Gambling Task (include GSR measures) (Bechara al. 1994)
Ppts presented with 4 virtual decks of cards on a computer screen
- told that each time they choose a card = will win some money
- every so often though, picking a card will lose them money
- sometimes cards will also have a penalty
some decks are bad decks and some decks are good decks - some lead to losses in long term and others lead to gains
FOUND;
- healthy: generally learned to avoid risky desks
- occipital/temporal/DLPFC regions lesions showed equivalent performance, preferring advantageous decks
What was the ‘Somatic Marker Hypothesis’ (Damasio)
Emotional info, in the form of physiological arousal, is needed to guide decision making
- somatic markers are the bodily reactions to emotional stimuli
OFC: supports learning of associations between somatic markers and complex situations
- ofc can use this info to assess outcomes of behavioural choices
Problems with the Iowa Gambling Task
Cards are presented in a fixed order that induces a preference for the risky decks
- subjects must OVERCOME this preference and switch to choosing good decks
- process of inhibition and switching is known as reversal learning
In variant of IGT that accounts for reversal learning (risky deck losses early)
- RL is not required
- suggests deficit is in reversal learning rather than value-based decision making
Reversal Learning Hypothesis - outline the role of the OFC
What it is: A cognitive process where an individual learns that a previously rewarded behavior is no longer rewarding and must adjust to a new rule or outcome.
Research into the OFC shows:
- OFC is necessary not so much for learning about stimulus based reward contingencies, but for UNLEARNING established associations
Outline the problems with the Reversal Learning Hypothesis of OFC Function (monkey study)
Monkeys with OFC lesions DON’T ALWAYS SHOW RL deficit
* The task in this study requires overcoming an innate preference for larger food rewards – quite different to a standard reversal learning task, which involves learning (and suppression) of arbitrary stimulus-outcome relationships * Rate of learning: monkeys took a long time to learn this task (50 sessions) whereas reversal learning takes place over much shorter periods of time * - OFC may only be required for reversal learning when stimulus-outcome computations are made ‘on the fly’ and suppression involves arbitrary stimulus-outcome relationships
Recent perspectives on OFC function emphasise the computation of value
* OFC serves as an ‘accountant’, converting information about outcomes (probability, magnitude, costs etc.) into a ‘common neural currency’ on which to base choices
* This may account for the role OFC seems to play in generation of complex emotions such as regret
OFC and counterfactual thinking - outline the neuropsychological evidence (Camille et al. 2004)
OFC patients did not show this pattern of counterfactual thinking – they didn’t modulate their ratings according to whether the alternative wheel would have been a win or lose.
Suggests a key role for the OFC in being able to EXPERIENCE the consequences of winning and losing, but more importantly to INTEGRATE INFORMATION from different sources of outcome
Summarise the role of the OFC in decision making
Facilitating effective decision making based on the knowledge of value of different actions
Suppressing actions based on recently learned action-outcome relationships
OFC seems necessary for value computations only when based on new information that changes rapidly
Ability to ‘mentally simulate’ information about predicted outcomes seems key here
What is the Striatum (Basal Ganglia)
The basal ganglia are a group of interconnected structures located deep within the brain that play a key role in movement control, habit formation, decision-making, and reward processing.
–> largest part is the striatum
What is dopamine (DA) + the dopamine receptors
Dopamine (DA) is a NEUROTRANSMITTER (chemical released to transmit electrical signal)
DA is produced by dopaminergic neurons in the VTA and SN in the midbrain
- several types, broadly categorised as D1-type and D2-type
D1: much more abundant in PFC
D2: much more abundant in striatum
What are the pathways that dopamine signalling occurs via
Mesolimbic
Mesocortical
Nigrostrial
Tuberoinfundibular
What is the role of dopamine in addiction
Modern theories emphasise learning and motivation over pleasure
- drugs of abuse enhance DA function by acting on midbrain neurons to transiently increase extracellular concentrations of DA
DA neurons in striatum encode reward prediction error - discrepancy between expected and gained reward
Prediction errors do play a key role in addiction
What is the role of dopamine in working memory/executive function
○ Brozoski (1979) – dopamine depletion in the PFC of monkeys causes a deficit in spatial working memory nearly as severe as complete ablation (removal)
○ Parkinson’s Disease: Gradual loss of dopamine neurons in the nigrostriatal pathway
§ Primarily a motor disorder - bradykinesia (slowed movement), akinesia (impairment of voluntary movement) and tremor
□ Currently no cure for PD although treatments include L-dopa (precursor of dopamine) and more recently deep brain stimulation
§ Studies in the 1980s/90s also found deficits in executive control functions in PD
Planning, working memory, attentional set-shifting (WCST), Stroop.
How does dopamine influence cognitive control - site theory
Suggests dopamine plays different roles depending on site of action
D1: more in PFC - function linked to stability of representations
D2: more in striatum - function linked to flexible behaviour
Dopamine might achieve balance of stability and flexibility by exerting different effects on striatal and PFC activation
What are the effects of ritalin on brain activation during reversal learning (Dodds 2008)
Researchers tested how methylphenidate (a dopamine booster) affects brain activity during a reversal learning task.
Participants had to pick the correct pattern from two options, using feedback (smiley for correct, sad face for wrong).
After a few correct choices, the correct pattern switched, requiring participants to adapt.
Result: Only the putamen (part of the striatum) showed changes in activity due to methylphenidate.
Conclusion: Dopamine in the striatum (especially the putamen) is crucial for cognitive flexibility (adapting to changing rules).
Outline the idea that basal ganglia acts as a ‘gate’ into the PFC
The basal ganglia, particularly the striatum, function as a gate that controls the flow of goal states into the prefrontal cortex (PFC). –> They maintain stable representations of current goals in the PFC but, when reward conditions change, dopamine signals in the basal ganglia inhibit old responses and enable the PFC to adopt new goal representations, allowing adaptive behavior.
*Evidence consistent with a DUAL ROLE FOR DOPAMINE
1. maintaining stability of responding (PFC)
2. enabling flexible switching (striatum)
Perhaps could account for IDs in traits that are risk factors for ADHD
Research: Cools (2007) - switching behaviour and neural activation in the striatum
Behavioural Data
- bromocriptine = increased switching behaviour in low-impulsive group
fMRI signal change in putamen
- much increased in bromocriptine group for HIGH impuslive group
Summarise the role of the striatum and dopamine in executive function
Striatum plays a key role in executive function
Parkinson’s disease: deficit in cognitive flexibility, suggesting a role for striatal dopamine
Effects of dopamine may depend on site of action
- striatum: cognitive flexibility
- PFC: cognivie stability
