Elevated gamma activity in left frontotemporal regions preceding sleep signals emotional arousal in Bipolar Disorders: Insights from a high-density EEG investigation

Background While changes in sleep architecture during depression and mania are well-established, the extent to which they persist during euthymia in Bipolar Disorders (BD) remains unclear. Here we investigate pre-sleep cortical arousal and its correlation with sleep architecture and subjective sleep quality in BD patients. Methods Subjective sleep measures and whole–night, high–density sleep electroencephalography (EEG) recordings were obtained from 16 euthymic BD patients and 16 age and sex-matched healthy control subjects. Sleep architecture was determined according to standard guidelines and power analysis was computed to compare mean group 0.5–80 Hz frequency bands in the EEG signal preceding sleep onset. Results Despite the absence of disturbances in subjective sleep, euthymic BD patients exhibited heightened sleep onset latency (52,91 ± 60,3 vs 21,76 ± 29,71, p = 0,018), REM density (2,65 ± 1,47 vs 1,52 ± 1,17, p = 0,022), and poorer sleep efficiency (0,64 ± 0,15 vs 0,74 ± 0,21, p = 0,032) compared to healthy controls. Total sleep time and durations of sleep substages did not differ between the groups. Additionally, our findings revealed increased pre-sleep gamma power in left frontotemporal areas among BD patients ( p = 0.005), which exhibited an inverse relationship with sleep efficiency that approached significance ( r = −0.497, p = 0.050). Conclusion Our findings suggest an alteration in sleep onset, efficiency, and REM density in euthymic BD patients, in the context of a preserved sleep duration. Some of these changes may be associated with a neural signature of cortical arousal that influences sleep quality.