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Phil McAndrew/The Cartoonbank/The New Yorker
Copyright © Bedford, Freeman & Worth Publishers.

Sleep loss affects our mood. Tiredness triggers testiness — more anger and conflicts (Keller
et al., 2019; Krizan & Hisler, 2019). Sleep loss also predicts depressive disorders (Palagini et al.,
®
AP Science Practice
2019). In two large studies, adolescents who slept 5 or fewer hours nightly had 70 percent and
Research Distributed by Bedford, Freeman & Worth Publishers. Not for redistribution.
80 percent higher risks of depression and suicidal thinking, respectively, than peers who slept
The statement that sleep loss 8 hours or more (Gangwisch et al., 2010; Whitmore et al., 2018). Among a half million people
predicts (as opposed to causes) from China, those who slept 5 or fewer hours a night had a more than doubled rate of depres-
depression implies correlational sion (Sun et al., 2018). This correlation appears to be one-way: When children and youth are
methods. Remember – as is
discussed in Unit 0 – correlation followed through time, sleep loss predicts depression, rather than vice versa (Gregory et al.,
does not mean causation! 2009). (To assess whether you are one of the many sleep-deprived students, see Table 1.5-1.)
REM sleep’s processing of emotional experiences helps protect against depression
(Walker & van der Helm, 2009). This may help to explain why parentally enforced bedtimes
predict less depression. Later secondary school start times consistently produce more sleep,
better and more on-time attendance, improved alertness, and fewer car accidents among
students (Bowers & Moyer, 2017; Foss et al., 2019; Morgenthaler et al., 2016). Thus, the
American Academy of Pediatrics (2014) advocates delaying adolescents’ school start times
to “allow students the opportunity to achieve optimal levels of sleep (8.5–9.5 hours).” As
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AP Exam Tip
psychologist Roxanne Prichard notes, “Nothing gets worse with better sleep, and a lot of
things get better” (Brody, 2018).
Make use of the psychological sci- When one psychology professor challenged students to sleep at least 8 hours each night
ence presented here. Be sure you
get a good night’s sleep before during final exams week, those who completed the challenge earned higher final exam
®
the AP exam! grades (Scullin, 2019). The bottom line: Sleep better to perform better.
Lack of sleep can also make you gain weight. Sleep deprivation messes with our hor-
mones, our metabolism, and our brain’s responses to food by
• increasing ghrelin, a hunger-arousing hormone, and decreasing its hunger-suppressing
partner, leptin (Shilsky et al., 2012).
• increasing cortisol, a stress hormone that stimulates the body to make fat, and decreasing
metabolic rate (Potter et al., 2017; Schmid et al., 2015).
• disrupting gene expression, which increases risk for heart disease and other negative
health outcomes (Möller-Levet et al., 2013; Mure et al., 2018).

104 Unit 1 Biological Bases of Behavior

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