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Task 4: Reward System (Kravitz et al. (cortico-striatal circuits…
Task 4: Reward System
Kravitz et al.
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addiction is installed wehn engagin other loops (cognitive, attentional and motor) than just corticostriatal loop
SUD = impaired DA receptor function in the striatum + associated reduction in baseline glucose metabolism in frontal and temporal cortices
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as D1-MSNs and D2-MSNs express different DA receptors, DA itself can exert different effects on each population
a) activation of the D1R enhances excitability, reward learning
b) activation of the D2R reduces excitability, reduced reinforcing value
Schultz
SUMMARY
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Reward uncertainty: slower, distinct electrophysiological repsonse
Unpredicted rewards + reward predicting stimuli = phasic burst of dopamine mediated activity = magnitude corresponding to reward
Aversive events: slow, electrophysiological dopamine depression reposnse
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PARADIGMS
conditioned inhibition paradigm = presenting 2 stimuli where one is associated wit "no reward" (this is the inhibitor) -> inhibitor and predictor elicts no reward, but just inhibitor elicts reward (prediction error=difference between actual reward and negative prediction from the inhibitor)
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Temporal-reward prediction error - displacing reward out of time produces reward related activity (both when too early and too late, but when too late we have initially a depression and then reward)
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Pollmann et al.
reward prediction error hypotesis (dopaminergic midbrain neurons respond at two timepoints during learing)
1, in repsonse to reward predicting cue/stimuli
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Willuhn et al.
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phasic dopamine release in DLS emerged progressively during the course of week of drug taking (while VMS dopamine signaling declined)
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DS = behavioural addiction - habit o performing behaviorthat increases the chance of getting cocaine (feedback no longer necesseart cause DS is engaged instead of VS) - DS regulates the automaticity of drug-taking responses
Striatal hierarchy - VMS lesion did not had effect on dopamine transmission in DLS but had a sleective effect on task-related signaling