Serotonergic neurons signal reward and punishment on multiple timescales

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Abstract

Serotonin's function in the brain is unclear. One challenge in testing the numerous hypotheses about serotonin's function has been observing the activity of identified serotonergic neurons in animals engaged in behavioral tasks. We recorded the activity of dorsal raphe neurons while mice experienced a task in which rewards and punishments varied across blocks of trials. We 'tagged' serotonergic neurons with the light-sensitive protein channelrhodopsin-2 and identified them based on their responses to light. We found three main features of serotonergic neuron activity: (1) a large fraction of serotonergic neurons modulated their tonic firing rates over the course of minutes during reward versus punishment blocks; (2) most were phasically excited by punishments; and (3) a subset was phasically excited by reward-predicting cues. By contrast, dopaminergic neurons did not show firing rate changes across blocks of trials. These results suggest that serotonergic neurons signal information about reward and punishment on multiple timescales.

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Jeremiah Y Cohen

Department of Molecular and Cellular Biology, Center for Brain Science, Harvard University, Cambridge, United States

For correspondence
jeremiah.cohen@jhmi.edu

Competing interests
The authors declare that no competing interests exist.
Mackenzie W Amoroso

Department of Molecular and Cellular Biology, Center for Brain Science, Harvard University, Cambridge, United States

Competing interests
The authors declare that no competing interests exist.
Naoshige Uchida

Department of Molecular and Cellular Biology, Center for Brain Science, Harvard University, Cambridge, United States

Competing interests
The authors declare that no competing interests exist.

Ethics

Animal experimentation: All surgical and experimental procedures were in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals and approved by the Harvard or Johns Hopkins Institutional Animal Care and Use Committees.

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This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.