Altered functional brain networks in isolated REM sleep behavior disorder during phasic REM sleep

Study objectives: Isolated REM sleep behavior disorder (iRBD) is characterized by vivid, emotionally charged, and often aggressive dreams, yet the underlying neural correlates remain poorly understood. This study aimed to investigate alterations in functional brain networks during REM sleep in iRBD patients using electroencephalogram (EEG), which is potentially associated with their dream characteristics. Methods: We analyzed EEG data from 13 drug-naïve iRBD patients and 10 healthy controls (HCs) during phasic and tonic REM sleep. Source-level functional connectivity was computed across 14 cortical regions associated with dream generation, and network topology was evaluated using graph theory metrics. Results: iRBD patients showed significantly increased gamma-band functional connectivity during phasic REM sleep (p = 0.003, network-based statistic). This hyperconnectivity correlated with reduced REM atonia (RAI; R = −0.725, p = 0.007) and trended with increased dream-related symptom severity. Key network hubs included the posterior cingulate cortex (PCC) and right inferior parietal lobule (rIPL)—core nodes of the default mode network—implicated in self-referential and spatial processing. Additionally, increased connectivity between rIPL and salience-motor circuits (anterior cingulate cortex, insula, and M1) may underlie emotional overactivation and aggressive dream content. Conclusion: Our findings suggest that gamma-band hyperconnectivity during phasic REM sleep reflects altered ‘dream-related network’ dynamics in iRBD, potentially contributing to the intensity and emotional valence of dream experiences. This study provides preliminary evidence that functional network alterations during REM sleep may shape dream characteristics in iRBD, offering new perspectives on its neurophysiological basis.