What Happens in the Brain and Body During Sleep?

When we don’t get enough sleep, it can affect how well we think and react — and even make us irritable or angry. In the long term, ongoing sleep deficiency raises our risk of some health problems, like heart disease and diabetes. It also affects how we learn, work and socialize with others.

Scientists have learned a great deal about the intricacies of sleep and how it supports a wide range of health activities. But there’s still much that we don’t know, especially about what happens in the brain and body during sleep.

In the past, people thought sleep was a time when the brain and body “shut down.” But researchers now know that both the body and the brain are active during slumber. They’re refining brain circuitry, clearing waste products and repairing damage, growing bones and muscles, regulating body temperature, and releasing hormones that control everything from your hunger to your stress levels.

People need between 7 and 8 hours of sleep each night to feel their best. But how much a person needs can vary by age and genetics. Some people are naturally short sleepers, while others can have difficulty falling or staying asleep. The reasons for these variations are not fully understood.

A big part of the challenge of getting enough sleep is balancing the demands of life, including work and family obligations. But the payoff is huge: Getting enough sleep supports healthy mental and physical health, and it makes it easier to maintain good habits like eating well, exercising regularly and not smoking.

In addition to boosting productivity, getting enough sleep promotes healthy emotions and strong relationships. It also helps to maintain a strong immune system, so you can fight off infections and stay healthy.

The first step to getting better sleep is establishing a regular bedtime and routine. Try to go to sleep and wake up at roughly the same times each day, avoiding bright lights and electronics close to bedtime. This can help your brain and body “train” to associate sleep with those times, helping you fall asleep faster and stay asleep longer.

Once you’re asleep, your body enters a series of distinct cycles that each last about 90 to 120 minutes. In the early stages of sleep, known as NREM 1, your brain wave activity slows down and your heart rate and breathing slow as well. You may experience hypnagogic jerks, which are little twitches that signal that you’re about to fall asleep.

As sleep progresses through NREM 2 and NREM 3, the hypnagogic jerks lessen, brain wave activity becomes more regular, and your muscle activity diminishes. You may also enter REM, the final stage of sleep. During this period, dreaming often takes place and is the most active part of sleep. REM typically makes up about 25% of total sleep time.