Is sleep affected after microgravity and hypergravity exposure? A pilot study.

Sleep is known to be affected in space travel and in residents of the international space station. But little is known about the direct effects of gravity changes on sleep, if other factors, such as sleep conditions, are kept constant. Here, as a first exploration, we investigated sleep before and after exposure to short bouts of microgravity and hypergravity during parabolic flights. Sleep was measured through actigraphy and self-report questionnaires in 20 healthy men and women before and after parabolic flight. Higher sleep fragmentation and more awakenings were found in the night after the flight as compared with the night before, which was discrepant from participants' reports showing better and longer sleep after the parabolic flight. Variable levels of experience with parabolic flights did not affect the results, nor did levels of scopolamine, a medication typically taken against motion sickness. Pre-existing sleep problems were related to sleep fragmentation and wake after sleep onset by a quadratic function such that participants with more sleep problems showed lower levels of sleep fragmentation and nighttime awakenings than those with few sleep problems. These novel findings, though preliminary, have important implications for future research, directed at prevention and treatment of sleep problems and their daytime consequences in situations of altered gravity, and possibly in the context of other daytime vestibular challenges as well.

Night-to-night variability in sleep and amyloid beta burden in normal aging.

INTRODUCTION: Alzheimer's disease is associated with sleep disturbances and accumulation of cerebral amyloid beta. The objective was to examine whether actigraphy-detected sleep parameters might be biomarkers for early amyloid burden. METHODS: Participants underwent a week of actigraphy and an amyloid positron emission tomography (PET) scan. Sleep duration and continuity disruption (sleep fragmentation and nocturnal awakenings) were extracted and compared between amyloid-positive and amyloid-negative participants. Then multiple linear regressions were used between mean or night-to-night intra-individual variability (standard deviation) of sleep parameters and brain amyloid burden in a voxel-wise analysis. RESULTS: Eighty-six subjects were included (80.3 ± 5.4 years; 48.8% of women). Amyloid-positive participants had a higher variability of sleep fragmentation compared to amyloid-negative participants. This parameter was associated with a higher amyloid burden in the frontal and parietal regions, and in the precuneus, in the whole sample. DISCUSSION: This study highlights the relevance of using variability in sleep continuity as a potential biomarker of early amyloid pathogenesis.