Insomnia disorder and hyperarousal: evidence from resting-state and sleeping EEG

Insomnia has become the second highly prevalent mental illness, secondary only to depression. The hyperarousal model of insomnia is one of the theories dedicated to clarifying the pathophysiological mechanism of insomnia disorder. The resting-state and sleeping EEG provide substantial evidence for this model. The current review firstly summarizes the analytic methods of the resting-state and sleeping EEG, and these methods can be mainly used to analyze the EEG data during wakefulness, sleep onset period and all sleep stages. Through literature review, we found that the EEG evidence of hyperarousal in insomniacs included impaired sleep continuity and architecture, enhanced frequency of arousal, delayed daytime sleep latency, and increased β activity during wakefulness and non-rapid eye movement sleep. Some interventions, such as cognitive behavioral therapy for insomnia, non-benzodiazepine hypnotics and slow oscillating transcranial direct current stimulation during sleep, turned out to be the effective therapies that could reduce the cortical hyperarousal in patients with insomnia. Power spectral analysis might aid in differentiating some insomnia subtypes, and could be used in the diagnosis and evaluation of the treatment response in patients with insomnia, but the confounding factors such as age, gender, and EEG band subdivision, should be considered. Future studies should focus on different insomnia subtypes, adopt a unified EEG band subdivision, and consider the possible interferences of patients’ age and gender. Based on the polysomnography derived sleep scoring, some meso/micro-analyses such as EEG source imaging and EEG time-frequency analysis should also be our primary concerns.