#Sleep

The final section of the book covers the many ways that modern life has impacted how much we sleep. The invention of the light bulb has allowed us to restructure our daily schedules at the cost of our natural sleep cycles. Exposure to electric lights in the evening shifts the timing of our sleep schedules due to a delayed release of melatonin leading to later bedtimes. The more constant environmental temperatures afforded by central heating and cooling also alter our ability to sleep by reducing natural temperature changes that help aid in sleep.

In chapters 9 - 11, Dr. Walker delves into the science of dreams. MRI scans taken while individuals dream during REM sleep show that certain areas of the brain, including those associated with spatial perception and emotion, are more active while individuals dream compared to during deep NREM sleep. Researchers have even been able to generally determine certain patterns of brain activity identified by an MRI in response to specific objects.

Part one of Why We Sleep closes with a summary of how sleep patterns change with age. Babies and young children exhibit polyphasic sleep, where they sleep in small doses throughout the day and night compared to older children and adults who have more regular monophasic sleep. As humans age, there is also a decrease in the amount of time spent in REM sleep and an increase in NREM sleep. This pattern highlights the importance of NREM sleep as a driver of brain maturation.

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.