Objective  To study the sleep electroencephalogram (EEG) power features of patients with chronic insomnia.

  Methods  Retrospective analysis was performed with patients who met the ICD-10 diagnostic criteria for chronic insomnia, using polysomnography (PSG) to examine the overnight sleep EEG. The sleep architectures and relative EEG power across five frequency bands during overnight sleep were compared to study the differences between the insomnia and control groups. Furthermore, the correlation between EEG power and various PSG measures was also analyzed.

  Results  Forty-five subjects were enrolled in the study, including 25 chronic insomniacs (18 females, aged 36.2±10.7 years) and 20 controls (18 females, aged 36.1±7.6 years). Compared to those of the control group, insomnia patients had significantly lower value of delta power (38.0±6.1 vs. 43.2±5.8, P<0.05) in the NREM1 stage, and increased value of beta power during total NREM, NREM1 and NREM2 (NREM sleep 5.4±2.3 vs. 3.8±1.4, NREM1 11.3±3.5 vs. 8.7±2.8, and NREM2 5.7±2.3 vs. 4.4±1.4, all P<0.05). For correlation analyses, in the insomnia group, a significantly positive correlation was found between the delta value during NREM sleep and the duration of NREM3 sleep (r=0.527). The beta value during NREM sleep was found to be negatively correlated to the duration of NREM3 sleep (r=－0.767). A positive correlation was found between the beta value during NREM sleep and the duration of NREM1 and NREM2 sleep (r=0.486 and 0.589, respectively).

  Conclusion  The results suggest that patients with chronic insomnia have decreased low-frequency EEG power, but increased high-frequency EEG power during NREM sleep. The findings indicate that cortex arousal level is elevated in chronic insomniacs during NREM sleep.