# Activity in human dorsal raphe nucleus signals changes in behavioural policy

## TL;DR

The study finds that the human dorsal raphe nucleus signals changes in behavior based on the reward environment.

## Contribution

The study demonstrates that DRN activity reflects changes in behavioral policy shaped by reward distribution.

## Key findings

- Activity in the dorsal raphe nucleus signals changes in behavioral policy based on reward distribution.
- Multivariate activity in dACC and AI tracks the relative value of reward opportunities.
- DRN, dACC, and AI form a circuit for behavioral policy changes.

## Abstract

The dorsal raphe nucleus (DRN) is an important source of serotonin to the human forebrain, however there is little consensus about its behavioural function. We build on recent results from animal models to demonstrate that activity in human DRN implements changes in behavioural policy that reflect the distribution of rewards in the environment. We use a foraging-inspired behavioural task to show that human participants change their policy to pursue or reject reward opportunities as a function of the average value of opportunities in the environment. Activity in DRN—but no other neuromodulatory nucleus—signals such policy changes. Patterns of multivariate activity in dorsal anterior cingulate cortex (dACC) and anterior insular cortex (AI), meanwhile, track the relative value of reward opportunities given the average value of the environment. We therefore suggest that DRN, dACC and AI form a circuit in which dACC/AI construct representations of reward opportunities given the current context, and DRN implements changes in behavioural policy based on these representations.

Activity in human dorsal raphe nucleus (DRN)—the main source of serotonin to the human forebrain—signals changes in behavioural policy that are shaped by the distribution of rewards in the environment.