All-night spectral and microstate EEG analysis in patients with Recurrent Isolated Sleep Paralysis (RISP)

Abstract

The pathophysiology of recurrent isolated sleep paralysis (RISP) has yet to be fully clarified. Very little research has been performed on electroencephalographic (EEG) signatures outside RISP episodes. This study aimed to investigate whether sleep is disturbed even without the occurrence of a RISP episode and in a stage different than conventional REM sleep. 17 RISP patients and 17 control subjects underwent two consecutive full-night video-polysomnography recordings. Spectral analysis was performed on all sleep stages in the delta, theta, and alpha band. EEG microstate (MS) analysis was performed on the NREM 3 phase due to the overall high correlation of subject template maps with canonical templates. Spectral analysis showed a significantly higher power of theta band activity in REM and NREM 2 sleep stages in RISP patients. The observed rise was also apparent in other sleep stages. Conversely, alpha power showed a downward trend in RISP patients deep sleep. MS maps similar to canonical topographies were obtained indicating the preservation of prototypical EEG generators in RISP patients. RISP patients showed significant differences in the temporal dynamics of MS, expressed by different transitions between MS C and D and between MS A and B. Both spectral analysis and MS characteristics showed abnormalities in the sleep of non-episodic RISP subjects. Our findings suggest that in order to understand the neurobiological background of RISP, there is a need to extend the analyses beyond REM-related processes and highlight the value of EEG microstate dynamics as promising functional biomarkers of RISP. Significance StatementWe focused on tracking electrophysiological traces of RISP (a REM parasomnia) beyond REM sleep of subjects clinically diagnosed with RISP outside of RISP episodes. We observed a rise of theta band activity in NREM 2 sleep of RISP patients. This may point to a larger dysregulation of sleep mechanism making the person more prone to sudden awakenings in the upcoming REM sleep. Theta band differences were further observed in REM sleep. We additionally utilized the EEG MS methodology on deep sleep to investigate differences in dominant brain topographies. Though dominant brain topographies are consistent with canonical MS, RISP patients show significantly different transitioning between sleep-related topographies suggesting a difference in their sleep regulation mechanisms.