EEG microstates during wake and NREM sleep in insomnia disorder.

Insomnia disorder (ID) is prevalent and debilitating, yet its neurophysiological basis remains unclear. Abnormalities in temporal parameters of electroencephalography (EEG) microstates have been linked to diverse neuropsychiatric disorders, but their dynamics across wakefulness and non-rapid eye movement (NREM) sleep in chronic insomnia remain unexplored. In this study, EEG microstate dynamics across wakefulness and NREM sleep were examined in adults with ID (n = 33) and healthy controls (HC; n = 29). Simultaneous EEG and functional magnetic resonance imaging (fMRI) were acquired during nocturnal sleep. Microstate parameters were tested for group differences, diagnostic classification, and associations with insomnia symptom course. Six stable microstates across stages were identified in ID. Linear mixed-effects models revealed significant interactions for Group × Map and main effects of Group on duration and occurrence of the microstates. Compared to HC, ID exhibited significantly shorter mean duration of microstates 1-3, and higher overall occurrence rates of microstates 4-6. The best-performing classifier achieved 90.0% accuracy in distinguishing ID from HC. The most influential predictor was the mean duration of Microstate 2, which was negatively associated with insomnia course. Together, these findings suggest stage- and map-dependent alterations in sleep microstate dynamics in ID, especially during N2 sleep.