Why We Sleep - Part One Summary

In part one, “This Thing Called Sleep,” Dr. Walker highlights sleep as a biological necessity and introduces us to basic sleep physiology. Inherently, we all know the importance of sleep but many of us do not know the true extent to which skimping on sleep or poor quality sleep affects our lives. Poor sleep is connected to complex health issues like weight gain as well as more obvious dangers such as traffic fatalities caused by driving while sleepy. There is even a rare genetic insomnia that onsets in midlife and gets progressively worse over the course of about a year until the patient passes away, proving that a lack of sleep will kill humans. The author closes his introduction to sleep by explaining the book is called Why We Sleep not because there is a single most important reason we need sleep but rather because sleep is complex and positively impacts almost every aspect of our physiology.

In chapters two and three, we learn about sleep regulation and how our modern lives alter our natural sleep rhythms. When light cues are removed, humans will follow a sleep-wake cycle that extends beyond 24-hours and features a slightly shorter evening sleep period as well as an afternoon nap. Caffeine and jet-lag are both two modern challenges that interrupt our circadian rhythm. Caffeine inhibits sleep pressure, the building feel of sleepiness throughout the day, by competitively binding to adenosine receptors which interferes with sleep pressure. When caffeine or other factors interrupt our sleep cycles, we experience more or less negative effects depending on the stage of sleep we lose the most of. 

Throughout the animal kingdom, every animal studied by sleep researchers sleeps. Worms even sleep, indicating that sleep predates vertebrates and may be an almost 500 million year old adaptation. There is currently no distinguishable trend for why certain species sleep for different amounts of time or vary the time spent in different sleep stages. Aquatic mammals and birds have some of the most interesting adaptations to ensure they obtain adequate sleep. Certain species will sleep with only half their brain at a time in order to obtain NREM sleep. When humans sleep, the sleep phase cycles between non-rapid eye movement (NREM) and rapid eye movement (REM) sleep. As our brains grew and we shifted from arboreal to terrestrial creatures, humans began to spend more time in REM sleep. This shift is thought to be one of the most important factors in allowing us to become the dominant and highly social species we are today.

Andi DeRogatis is a graduate student at UC Davis in the animal biology graduate group. She is currently studying how the avian immune system is influenced by the process of molt. She loves all things birds and is passionate about getting others excited about birds as well! You can follow her on Twitter @AndiDerogatis.

Lindsey Mooney is a graduate student in the UC Davis Psychology Department. You can follow her on Twitter @Linz_Mooney.

For more content from the UC Davis science communication group "Science Says", follow us on Twitter @SciSays.