Analysis of eeg functional connectivity prior to somnambulism

Introduction There has been increased interest in examining sleep EEG data in terms of functional brain connectivity. These new investigative tools, however, remain practically unexplored in relation to sleep disorders. We studied the EEG coherence and interdependencies between brain areas before the onset of somnambulistic episodes recorded in the sleep laboratory. Materials and methods 13 adult sleepwalkers were investigated with polysomnography. Patients were selected on the basis of having experienced a somnambulistic episode in the sleep laboratory during their first period slow-wave sleep (SWS). The 20 s immediately preceding the onset of each of the 13 episodes was compared to the 20 s occurring two minutes prior to these episodes’ onset. Data from the Fp1, Fp2, F3, F4, C3, C4, P3, P4, O1, O2 leads were investigated using two complimentary measures of brain connectivity: standard coherence and imaginary coherence (the latter addressing the problem of spurious correlations due to common sources). Results The largest observed difference between the 20 s periods occurring immediately prior to episode onset versus the 20 s segments occurring 2 min before episode onset was for the imaginary coherence with greater connectivity taking place immediately preceding sleepwalking episodes. Furthermore, increased connectivity was strongest between frontal and occipital brain areas. Conclusion These pilot findings suggest that episodes of somnambulism are preceded by temporal changes in brain connectivity and that the a direct interdependence between frontal and occipital brain regions may be implicated. The study of EEG connectivity in relation to NREM parasomnias may help elucidate brain processes underlying episode occurrence. Acknowledgements This research was supported by research grants from the Fonds de la recherche en sante du Quebec (FRSQ) and from the Canadian Institutes of Health Research (CIHR).