Embracing sleep-onset complexity.

The sleep-onset period (SOP), the transition from wakefulness to sleep, has been largely overlooked despite its potential importance. This review synthesizes current knowledge about the SOP in humans, examining its definition and limits, the dynamic electrophysiological changes that accompany falling asleep, and the interplay between internal and external processing during this transition. The authors propose that the SOP may offer cognitive benefits and identify novel directions for better diagnosing sleep-onset disorders. The review highlights recent findings that have reignited interest in this transitional period, shedding light on its neural mechanisms, cognitive dynamics, and clinical implications.

Study at a glance

Abstract

Sleep is crucial for many vital functions and has been extensively studied. By contrast, the sleep-onset period (SOP), often portrayed as a mere prelude to sleep, has been largely overlooked and remains poorly characterized. Recent findings, however, have reignited interest in this transitional period and have shed light on its neural mechanisms, cognitive dynamics, and clinical implications. This review synthesizes the existing knowledge about the SOP in humans. We first examine the current definition of the SOP and its limits, and consider the dynamic and complex electrophysiological changes that accompany the descent to sleep. We then describe the interplay between internal and external processing during the wake-to-sleep transition. Finally, we discuss the putative cognitive benefits of the SOP and identify novel directions to better diagnose sleep-onset disorders.