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Poster C137 in Poster Session C - Friday, August 9, 2024, 11:15 am – 1:15 pm, Johnson Ice Rink
Expectancy-related changes in the firing of dopamine neurons depend on the hippocampus
Zhewei Zhang1, Yuji Takahashi1, Marlian Montesinos-Cartegena1, Thorsten Kahnt1, Angela Langdon2, Geoffrey Schoenbaum1; 1National Institute on Drug Abuse, 2National Institute on Mental Health
The orbitofrontal cortex (OFC) and hippocampus (HC) both contribute to cognitive maps that support flexible behaviors. Previously, we recorded dopamine neurons in sham and OFC-lesioned rats performing an odor-based choice task, in which reward prediction errors (RPEs) were induced by manipulating the expected reward across blocks. We found that OFC supports dopaminergic RPEs in the VTA, particularly when those errors depend on hidden or inferred information. Here we extended this approach to examine the contribution of the HC. Dopamine neurons recorded from ipsilateral HC lesioned rats showed intact responses to the odor cues, but not to the delivery and omission of rewards. To explain these phenomena, we developed a hierarchical temporal difference reinforcement learning model in a partially observable semi-Markov framework. By assuming HC is necessary for estimating the upper-level hidden states that distinguished the trial blocks, we successfully reproduced the results observed in HC-lesioned rats. The results contrast the respective roles of the OFC and HC in cognitive mapping and demonstrate that dopamine neurons access a rich set of information from distributed regions.
Keywords: dopamine hippocampus learning reward prediction error