Individual alpha frequency before the sleep onset: towards a personalized neurophysiological characterization of insomnia

Objective: This study investigated the electrophysiological features of the alpha band and Individual Alpha Frequency (IAF) before the Sleep Onset (SO) period in Insomnia Disorder patients (ID) and Healthy Controls (HCs). We hypothesized that IAF, as an individualized electrophysiological marker rather than broadband alpha power, could better capture individual sleep-initiation alterations characterizing ID and Sleep State Misperception (SSM). Methods: Polysomnographic recordings were analyzed to assess changes in alpha activity and IAF Before-SO in occipital regions. Correlational analyses were conducted to investigate associations between the alpha activity, IAF, sleep parameters, and SSM. Results: Compared to HC, ID patients showed higher occipital IAF power during the Before-SO, while no group differences emerged in the broadband alpha activity. Correlational analyses revealed that faster IAF was associated with longer sleep latency and delayed transition to deep sleep, whereas higher IAF power was related to greater insomnia severity and stronger SSM. Conclusions: These findings suggest that IAF during the period preceding the SO is a sensitive marker of cortical arousal, contributing to impaired sleep initiation and distorted sleep perception. Significance: These findings underscore the potential role of the IAF as an electrophysiological marker of ID pathophysiology and a target for personalized therapeutic interventions.