A good night’s sleep can help you hit the reset button after a tough day, improve your outlook and mood, and better prepare for what’s next. But a lack of rest is also linked to an array of health problems, including depression, obesity, diabetes, and heart disease. That’s why it’s important to prioritize sleep.
A growing body of evidence shows that sleeping is more than just a way to get through the day. During slumber, our brains lock memories in our brains, help us regulate emotions, and even boost the immune system to fight off infections. Then there’s the fact that getting enough sleep is key to maintaining a healthy weight and reducing the risk of conditions like heart disease, cancer, and dementia.
When you’re asleep, your muscles are at their most relaxed, and blood flow to the brain slows. Your heart rate and breathing also slow down, and you enter a deep sleep state known as stage 2. This is the most difficult to wake up from and is the stage where sleepwalking, bedwetting, and dreaming occur. It is also the period when people experience sleep apnea, nightmares, and insomnia.
During a sleep cycle, the brain shifts between two different states: the relatively deactivated NREM phase and the active REM phase. While the NREM phase accounts for most of a sleeper’s time, REM typically takes up about 20 percent of the total sleep time. The brain’s activity during REM is more variable than that of NREM, and the pattern of sleep changes over the course of one night and between individuals.
Many of the early breakthroughs in sleep research came from the lab of University of Chicago Prof. Nathaniel Kleitman, who pioneered all-night electroencephalogram (EEG) recordings of human sleep. The data enabled researchers to chart the progression of sleep stages and cycles over the course of the night. Then, using brain-imaging studies, they could correlate those patterns with the behavior and physiological responses of the subject.
The study of sleep is an interdisciplinary field, drawing upon the disciplines of psychology, neuroscience, medicine, economics, public health, and history. It involves a range of methods, from behavioral observation to psychological testing, to genetics and molecular biology. Some of the most significant discoveries in this area have been made by combining data from several different fields and by thinking creatively about new ways to approach old questions.
During a normal sleep cycle, a person spends six or seven periods of sleep, alternating with waking periods. This recurrent alternation is characteristic of mammals, birds, and certain closely related reptiles. The occurrence of recurring, spontaneous periods of inactivity and reduced reactivity, however, is not universal among mammalian species, and subjective judgments of sleepiness can often contradict both behavioral classification and physiological measurements. This raises interesting questions about what is and is not sleep.