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Many thanks to Brandon Hidaka for a very wakeful synopsis on the SLEEP session!

David Samson began this stimulating session with a presentation about how sleep behavior differs between WEIRD (Western, Educated, Industrialized, Rich, Democratic) humans and a group of people living without electricity in Madagascar. Using data collected by actigraphs, he showed that the WEIRD group had greater sleep duration and quality, which was contrary to the hypothesis that modernization is associated with poorer sleep. The non-electric group spent an average of 2 hours in bed not asleep. However, Samson et al. also observed that the non-electric group exhibited decreased variability of sleep onset and awakening, which may indicate enhanced circadian synchronicity with the environment. Napping frequency and duration was also greater among the non-electric group. Overall, there was no difference in total sleep duration between groups. In conclusion, there appear to be tradeoffs from changes in sleep patterns from modernization in that WEIRD people have more consolidated, uninterrupted sleep, while those with more ancestral lifestyles have more consistent circadian rhythms.

Virginia Vitzthum next presented her research into the sleep patterns of mother-infant dyads in a group living in the Bolivian highlands, either near to or far from a large city. She and her colleagues found that night-feeding frequency is steady until about 1yr of age and then steadily declines thereafter. More nighttime feeding was associated with an earlier rise from bed. Those living near town tended to go to bed later. She finally showed that living near town modified the relationship between infant age and maternal sleep, wherein rural mothers slept more as the baby ages, but maternal sleep did not change over time for mothers living near town. Her research provided interesting insight of how breastfeeding is related to maternal sleep in traditional societies.

Randy Nesse presented the hypothesis that vulnerability to Alzheimer’s disease (AD) is a tradeoff of sleeping less as a species. The following evidence supported the idea: (a) humans sleep less than other primates, (b) AD is absent in other primates, (c) the brain regions most severely affected in AD are also the regions that have undergone the most recent evolutionary change, (c) amyloid-beta is cleared at a greater rate by the brains glymphatic system during sleep, (d) decreased sleep is characteristic of, and possibly a risk factor for, AD, (e) melatonin inhibits the fibrillization of amyloid-beta, and (f) the elderly have lower melatonin levels and poorer/less sleep than younger humans. It was creative connection of ideas from many different fields of science.

The final presentation of the session from Ghandi Yetish shared results from an analysis of how sleep structures in the Tsimane hunter-horticulturalists relate to sleep quality and duration. He and his colleagues found that sleeping without four walls was associated with waking as a consequence of animal noises. Interestingly, sleeping in an enclosed space with walls was not associated with greater total sleep time, but it was associated with greater variance of time going to bed, total sleep time, and sleep efficiency. It was also observed that children were the most common cause of sleep disturbance, even more so for those sleeping without walls. He concluded by the evolutionary framework that sleep is a time of vulnerability that merits increased vigilance in less safe structures.

With such diversity of interesting presentations, the session gave everybody something to sleep on.