Resting-state quantitative EEG characteristics of insomniac patients with depression.

Insomnia is known to show hyperarousal in the central nervous system. However, depression that often coexists with insomnia exhibits hypo-activity in the frontal lobe, which is very different from insomnia. In the present study, we examined wake resting state EEG of insomniac patients with depression to investigate whether they could be conceptualized as spectrum of insomnia or significantly different from insomnia. We compared the absolute power values of EEG spectra of three groups: 15 insomniacs with comorbid depression (CD), age- and sex-matched 15 comorbid-free insomniacs (CFI), and 15 good sleep controls (GSC). As a result, CD and CFI showed no significant difference in the EEG power spectrum analysis. Compared with GSC, however, both CD and CFI groups showed increased high frequency EEG amplitude. From these results, we have confirmed that CD shows cortical hyperarousal similar to insomnia in the daytime resting state. In conclusion, it would be reasonable to understood insomniac patients experiencing depression as a continuum of insomnia patients.