Dopamine Modulates Adaptive Prediction Error Coding in the Human Midbrain and Striatum.

Area of Science:

• Neuroscience
• Computational Psychiatry
• Decision Science

Background:

• Optimal reward prediction requires adapting to fluctuating reward values.
• Adaptive coding of prediction errors, relative to reward variability, facilitates efficient learning.
• Dopamine neurons in the midbrain are implicated in adaptive coding, with emerging human fMRI evidence.

Purpose of the Study:

• To investigate the direct effect of dopaminergic system perturbations on adaptive prediction error coding in humans.
• To examine the role of dopamine in learning to predict rewards from variable distributions.

Main Methods:

• A placebo-controlled, between-subject pharmacological fMRI study using a dopaminergic agonist (bromocriptine) and antagonist (sulpiride).
• Participants performed a reward prediction task with varying reward variability (standard deviations).
• Trial-by-trial prediction errors were recorded, and brain activity was measured using fMRI.

Main Results:

• Sulpiride (dopamine antagonist) attenuated adaptive coding in the midbrain and ventral striatum, decreasing performance.
• Bromocriptine (dopamine agonist) did not significantly impact adaptive coding or performance.
• Computational modeling indicated reduced behavioral adaptation in the sulpiride group despite no group differences in performance variability.

Conclusions:

• Normal dopaminergic function is critical for adaptive prediction error coding and efficient learning in variable environments.
• Dopamine perturbations, particularly antagonism, impair the neural and behavioral adaptation to reward variability.
• Findings offer insights into the role of dopamine in mental illnesses associated with dopaminergic dysfunction, such as psychosis.