Aperiodic and periodic components of resting-state EEG in primary insomnia

Insomnia is one of the most prevalent health concerns within the general population, with a multitude of existing electroencephalographic (EEG) spectral studies supporting heightened levels of high-frequency EEG activity as an index of cortical arousal. Nevertheless, traditional spectral analysis has been limited by its inability to distinguish between aperiodic and periodic elements. In contrast, a novel method, Spectral Parameterization (SpecParam), can separate these components and reveal the neural mechanisms of cortical arousal.

The aperiodic and periodic activities of 42 insomnia disorder (ID) patients and 45 age- and sex-matched healthy controls (HC) were evaluated during eyes-closed resting state. The associations between behavioral scales and aperiodic/periodic parameters were further examined to elucidate the underlying psychophysiological significance.

We found that the aperiodic exponent was diminished in the ID group compared to the HC group. Additionally, the ID group exhibited an elevated central frequency and a more constrained bandwidth for periodic activity within the alpha band. Within-group correlation analyses revealed that a reduced exponent was associated with worse sleep quality and more frequent failures in inhibitory control within the ID group.

A smaller exponent within the ID group may reflect impaired inhibitory neuronal activity, potentially leading to cortical hyperarousal. The association of a smaller exponent with deteriorated sleep quality and impaired inhibitory control supports this hypothesis. Furthermore, the increased center frequency of the alpha band across extensive brain regions, along with a narrower alpha bandwidth in the left frontal and right parieto-occipital regions, may represent abnormal manifestations associated with excessive arousal. In summary, these results support the role of aperiodic activity as an index of impaired excitation/inhibition balance in neural activity within in ID group.