M. MB Grivette, A. Betts, A. Rockhill, N. Swann, A. Lovering

1University of Oregon, Eugene, OR

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 mechanism leading to SANS is 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 5/11 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 an electrophysiological biomarker to identify those at risk for developing SANS during long duration spaceflight. METHODS: Power spectral density (psd) was calculated using the MNE 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. RESULTS: There were significant differences during non-rapid eye movement (NREM) stage 2 sleep in alpha power, in addition to low and high beta power. CONCLUSION: Blunted alpha and beta activity during N2 sleep could suggest increased risk for developing SANS.

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