Power Spectrum of Brain Activity During Sleep and Development of Spaceflight Associated Neuro-ocular Syndrome
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Date
2023-05
Authors
Grivette, Margaret
Journal Title
Journal ISSN
Volume Title
Publisher
University of Oregon
Abstract
Approximately 70% of astronauts returning from 4-6 months of spaceflight present lasting neuro-ocular changes including retinal thickening, cotton wool spots, and optic disc edema among others. This syndrome of findings is termed Spaceflight Associated Neuro-Ocular Syndrome (SANS). Although the underlying mechanisms leading to SANS are unclear, reduced metabolic clearance of neuro-ocular structures may play a role, and neurometabolic clearance occurs primarily via the glymphatic system that is most active during sleep. Sleep is known to be disrupted in spaceflight despite hypnotic drug use. Recently our group utilized a strict head-down tilt bed rest model (spaceflight analog) to induce findings of SANS. We found that 5 out of 11 subjects developed optic disc edema and, those who developed these ocular changes were shorter sleepers prior to, during, and after bed rest. Differences in sleep duration and sleep intensity are expected to result in unique electroencephalographic (EEG) activities. Thus, examining the EEG activity in those who do and do not develop optic disc edema may provide electrophysiological biomarkers to identify those at risk for developing SANS during long duration spaceflight. Power spectral density (psd) was calculated using the MNE (Minimum-Norm Estimate) psd function in Python. Power values were averaged over conventional frequency bands (delta: 1-4 Hz, theta: 4-8 Hz, alpha: 8-13, low beta: 13-21, high beta: 21-35). A three-factor repeated measures ANOVA was used to test differences in sleep stages for each frequency range and channel across all participants and compared to a Bonferroni adjusted alpha. There were significant differences in alpha and low and high beta power during non-rapid eye movement (NREM) stage 2 sleep; participants who did not develop optic disc edema had greater alpha and beta power compared to those who did develop optic disc edema. Blunted alpha and beta activity during N2 sleep could suggest increased risk for developing SANS.
Description
35 pages
Keywords
astronaut health, Spaceflight Associated Neuro-ocular Sydrome, SANS, power spectral analysis, sleep physiology