Raphe nuclei in cognition: A network-level framework for behavioral-state control.

Adaptive behavior requires organisms to maintain, update, and switch between behavioral states as environmental conditions change. The raphe nuclei (RN), best known as a major source of forebrain serotonin, have long been linked to arousal, inhibition, patience, affect, and flexibility, but these functions have often been considered separately. Here, we argue that recent advances in circuit tracing, cell-type-specific manipulation, high-resolution neuroimaging and neurostimulation, and computational modeling support a more integrated view in which RN are embedded within distributed cortico-subcortical and neuromodulatory networks. Across species, RN activity tracks environmental statistics such as value, uncertainty, threat, and reward context and contributes to transitions between motivational and cognitive states. We propose a network-level framework in which RN regulate when behavioral states should persist, update, or switch.