What We Know About Sleep
The study of sleep is a rich and multifaceted field. It is a key to many of the body’s processes, including energy production, digestion, and immune function. It also influences memory, mood, and creativity. Scientists spend much of their waking lives studying this fundamental and critical process, and we are just beginning to understand its complexities. Here are some of the key things we know about sleep:
The human brain is not at rest during sleep. In fact, it’s probably doing more work during sleep than when you are awake. For example, sleep appears to strengthen memories and help us recall them, and it may even make you more creative (see a recent study in Science Advances). In addition, during sleep the brain clears away toxins and proteins linked to Alzheimer’s disease twice as fast as when you are awake.
Insufficient sleep is associated with a host of problems, such as a decrease in attention and cognitive processing, a higher risk of motor vehicle crashes and other accidents, high blood pressure, depression, and anxiety. It can also impair the immune system, making the body more susceptible to infections and a less effective defender against them. Sleep is vital for the growth and development of children, and lack of sufficient sleep in young people is often a cause of difficult behavior, poor eating patterns, and weight gain.
When most of us think of “sleep,” we picture a state of dormancy, during which our bodies and minds are largely unengaged. But this could not be more inaccurate. Scientists are discovering more and more about the many functions of sleep, and they continue to uncover surprising secrets.
The brain is active during sleep, and the body cycles through four stages of non-rapid eye movement (NREM) sleep each night. The first three of these stages are progressively deeper, while the fourth stage, rapid eye movements (REM) sleep, is associated with dreaming. It’s no surprise that humans evolved to sleep in a consolidated block each night, allowing them to avoid predators and conserve energy while meeting their need for rest.
Researchers have used all-night electroencephalogram (EEG) recordings to study the sequence of brain activity that occurs during the sleep cycle, and a number of important discoveries have been made. One of the most significant is that, while all animals seem to sleep, not all of them sleep the same way. This reflects the complexity of sleep, with both global and local factors influencing its occurrence and intensity (Krueger et al., 2021).
Scientists have identified a variety of different sleep phases, each of which is characterized by specific patterns of neural activity. A leading hypothesis is that slow waves, a major feature of all sleep stages, are generated and regulated locally in small cortical networks. It is thought that this is the reason why sleep appears to be a universal phenomenon, rather than specific to humans or other mammals. However, this has yet to be proven.