Global sleep crisis

A global quantification of “normal” sleep schedules using smartphone data
Olivia J. Walch, Amy Cochran and Daniel B. Forger
Science Advances 06 May 2016:Vol. 2, no. 5, e1501705

The influence of the circadian clock on sleep scheduling has been studied extensively in the laboratory; however, the effects of society on sleep remain largely unquantified. We show how a smartphone app that we have developed, ENTRAIN, accurately collects data on sleep habits around the world. Through mathematical modeling and statistics, we find that social pressures weaken and/or conceal biological drives in the evening, leading individuals to delay their bedtime and shorten their sleep. A country’s average bedtime, but not average wake time, predicts sleep duration. We further show that mathematical models based on controlled laboratory experiments predict qualitative trends in sunrise, sunset, and light level; however, these effects are attenuated in the real world around bedtime. Additionally, we find that women schedule more sleep than men and that users reporting that they are typically exposed to outdoor light go to sleep earlier and sleep more than those reporting indoor light. Finally, we find that age is the primary determinant of sleep timing, and that age plays an important role in the variability of population-level sleep habits. This work better defines and personalizes “normal” sleep, produces hypotheses for future testing in the laboratory, and suggests important ways to counteract the global sleep crisis.

Sex Differences in Cognitive Estimation

Sex Differences in Cognitive Estimation During Sleep Deprivation: Effects of Stimulant Countermeasures
Int J Neurosci 2008;118(11):1547-57.

Stimulant medications restore simple alertness during sleep loss, but it is not clear how they affect complex executive functions, particularly in light of sex differences in cerebral organization. The effectiveness of caffeine, modafinil, dextroamphetamine, or placebo for sustaining performance on the Biber Cognitive Estimation Test (BCET) was compared in 29 men and 25 women following 46 hr of sleep deprivation. Stimulants had differential effects on BCET performance as a function of the sex of the subjects. Women receiving placebo or caffeine scored significantly worse than males, while modafinil and dextroamphetamine were effective at sustaining BCET performance of men andwomen.