Cell-type-specific encoding of effort-based decision-making in the dorsal raphe nucleus

Effort-based decision-making, the process of weighing reward benefits against effort costs, is essential for adaptive behavior. Although the dorsal raphe nucleus (DRN) contributes to reward processing and effort-related behaviors, how specific DRN neuronal subtypes contribute to effort-based decision-making remains poorly understood. Using fiber photometry to record DRN serotonergic and GABAergic neurons during an effort-based decision-making task, we found that tonic fluctuations in DRN serotonergic activity were selectively associated with persistent selection of the high-value option. Furthermore, we found that while neither neuronal population was sensitive to relative reward magnitude, effort expenditure selectively enhanced decision- and reward-related signals carried by serotonergic and GABAergic neurons, respectively. Together, these findings support a cell type-specific model in which serotonergic activity provides a signal linking persistent motivational states to effortful choice, whereas GABAergic activity may contribute to evaluating or updating reward outcomes after effort expenditure. SIGNIFICANCE STATEMENTChoosing whether a reward is worth the effort required to obtain it is essential for adaptive behavior, yet the neural mechanisms underlying this process remain incompletely understood. Here, we identify distinct contributions of serotonin- and GABAergic neurons in the dorsal raphe nucleus, a major source of brain serotonin, to effort-based decision-making. Serotonergic neurons were preferentially engaged in sustained motivational state and action selection, and GABAergic neurons in the processing of reward outcomes following costly actions. Our findings reveal a cell type-specific organization of effort-based reward seeking in the dorsal raphe nucleus and provide a framework for understanding how motivational states, decisions, and reward outcomes are coordinated.