The Role Of Serotonin In Sleep And Mood Regulation: A Comparative Physiological Review Of Healthy And Depressed Populations

Abstract

Serotonin (5-hydroxytryptamine, 5-HT) plays a critical rolein synchronizingsleep architecture and emotional regulation. Although its influence on mood and sleep has been extensively studied individually, their integrated physiological regulation,and how its disruption contributes to depression,remains insufficiently explored. This review presents a comparative physiological analysis of serotonergic function in healthy versus depressed individ- uals, emphasizing how serotonin rhythms, receptor dynamics, and neural circuits coordinate sleep-wake cycles and mood stability. In healthy individuals, serotonin follows a distinct circadian rhythm. Daytime increases support arousal and emotional resilience, while nighttime declines facilitate sleep onset and progression through sleep stages. In depression, these rhythms become flattened. Serotonin synthesis decreases, receptor sensitivity changes, and neural circuits lose coherence. These alterations contribute to fragmented sleep, shortened REM latency, and persistent mood instability. Synthesizing evidence from neuroanatomy, receptor pharmacology, and circadian physiology, this review pro- poses the Serotonergic Synchronization Failure Model, conceptualizing depression as a breakdown in serotoner- gic integration across sleep and mood systems. This perspective reframes depressive symptoms not as isolated dysfunctions but as interconnected failures of physiological synchrony. The analysis underscores the need for therapeutic interventions, pharmacological, behavioral, and circadian-based,that restore serotonergic coher- ence to improve both sleep and mood regulation.