According to the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM‐V), insomnia disorder (ID) is defined as difficulty initiating/maintaining sleep, waking too early, and/or nonrestorative sleep. The “hyperarousal” model suggests that ID patients are in neurobiological and psychological states of excessive alertness, as reflected by cortical hyperexcitability during both wakefulness and sleep (Lanza, DelRosso, & Ferri, 2022). Cortical hyperexcitability alters neuronal firing patterns and manifests as abnormal neural oscillations (Fernandez‐Mendoza et al., 2016; Huang et al., 2012; Riemann et al., 2010; van der Werf et al., 2010). Previous electroencephalography (EEG) studies mostly used spectral analysis to characterize abnormal neural oscillations in ID patients, that is, higher beta and gamma powers and lower delta, theta, and alpha powers (Merica et al., 1998; Zhao et al., 2021). However, some EEG studies on ID have failed to observe significant differences in spectral power between ID patients and good sleeper controls (GSC) (Chen et al., 2014; Kang et al., 2018; Wu et al., 2013). Therefore, a more reliable and sensitive indicator is required to quantify the abnormal neural oscillations in ID.
