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.