Activity in human dorsal raphe nucleus signals changes in behavioural policy

Area of Science:

• Neuroscience
• Cognitive Science
• Behavioral Economics

Background:

• The dorsal raphe nucleus (DRN) is a key serotonin source in the human forebrain, but its behavioral functions remain debated.
• Previous animal studies suggest a role for the DRN in behavioral regulation, yet direct evidence in humans is limited.

Purpose of the Study:

• To investigate the role of the human dorsal raphe nucleus (DRN) in implementing changes in behavioral policy.
• To determine how DRN activity relates to reward value and environmental context.
• To elucidate the functional circuit involving the DRN, dorsal anterior cingulate cortex (dACC), and anterior insular cortex (AI) in decision-making.

Main Methods:

• Utilized a foraging-inspired behavioral task in human participants.
• Employed neuroimaging techniques to measure brain activity, focusing on the DRN, dACC, and AI.
• Analyzed neural activity patterns in relation to behavioral choices and environmental reward statistics.

Main Results:

• Human participants adjusted their behavioral policy to pursue or avoid reward opportunities based on the average environmental reward value.
• Activity within the DRN specifically signaled these policy changes, distinguishing it from other neuromodulatory nuclei.
• Multivariate activity in the dACC and AI tracked the relative value of reward opportunities within the current environmental context.

Conclusions:

• The human DRN plays a critical role in implementing adaptive behavioral policy changes in response to environmental reward structures.
• A circuit comprising the DRN, dACC, and AI dynamically represents reward opportunities and context to guide behavior.
• The dACC and AI likely construct context-dependent reward representations, which the DRN utilizes to enact behavioral policy adjustments.