EEG in insomnia disorder: novel findings and future directions

: Electrophysiological studies have played a crucial role for the present conceptualization of Insomnia Disorder (ID) as a 24-h disorder characterized by hyperarousal expressed during wakefulness and sleep. In this Opinion piece, we highlight novel findings and delineate relevant future directions in the field of electroencephalographic (EEG) assessment in ID. Prolonged home recordings are crucial to provide ecological assessment also considering night-to-night variability. High-density EEG allows the description of local frequency-specific electrophysiological alterations in ID. A multimodal approach, combining EEG with neuroimaging techniques and non-invasive brain stimulation, may be informative about the neurophysiological mechanisms underlying ID and guide the development of targeted therapeutic strategies. Also, we highlight the need for longitudinal studies in this field. Novel approaches to quantitative EEG are represented by the assessment of aperiodic components and genuine oscillatory events. Finally, emerging research avenues include the assessment of sleep EEG hallmarks (e.g., sleep spindles and K-complexes) beyond their mere quantification, the application of artificial intelligence for automated identification and subtyping of ID, and EEG-based functional connectivity.