Δ∨ (change in predictive value) = αβ(salience)(λ(US)- ∨(predictive value)
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Tonic
Sustained Release
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Phasic
bursts
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Fiorillo (2003)
sustained dopamine firing especially for uncertain trials (0.5/50%)
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Ramnianania used fMRI to examine
1) failure of expected reward 2) occurance of unexpected reward
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Results showed...
changes in anterior prefrontal cortex in relation to both types but in the medial orbitofrontal cortex that are specific to the presentation of unexpected reward - actively encode the associations between them
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Temporal Difference Errors are used to predict
a measure of the total amount of reward expected over the future (INCLUDE TIME)
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Unexpected reward leads to ... while a unexpected reward ommision leads to
1) positive PE response at reward delivery 2) negative PE response
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Odoherty wanted to see...
if the ventral stritum, orbitofrontal cortex or other brain regions were consisten with TD pre
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Odoherty results
Backward shift in the hemodynamic response in the ventral striatum over the course of learning. Response in the ventral striatum, orbitofrontal cortexm cerebellum, inferior frontal sulcus, inferiour frontal gyrus
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Rolls - reward magnitiude found that
TD error correlated with Nucleus Accumbens, IFG and midbrain activity
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changes in what were used as regressors in the fMRI model
EV, RM and TD
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Ventral striatum and midbrain are correlated in
probabilistic decision-making task with TD error , activation in teh insula may be also related to decision making -> low EV
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Kumar- MDD found that
significantly reduced reward-learnign signals in : Ventral striatum, rostral, dorsal anterior cingulate, retrosprienial cortex, midbrain and hippocampus. TD signal was increase in brainstem of patients.
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