What Happens During a Good Night’s Sleep?

Sleep gives your body and brain the time they need to rest and rebuild. It allows your short-term memories to be converted into long-term ones, and is vital for your mental health and learning ability. It also helps you to maintain a healthy weight and ward off diseases like heart disease, diabetes and high blood pressure.

Humans evolved to live on a planet with a 24-hour day-night cycle, and the biological patterns that help us live in sync with it are known as circadian rhythms. These work alongside the “sleep drive,” a natural desire that builds throughout the day until you feel it’s time to go to bed.

But modern living has disrupted these natural patterns for an estimated 50-70 million people in the United States alone. The lights and sounds of TVs, computers, smartphones, overnight and irregular shift work, and traveling across multiple time zones all affect the quality and length of your sleep. Over time, insufficient sleep can cause serious physical and psychological problems.

Getting adequate amounts of sleep is critical for your physical and mental well-being, but it’s not always easy. In addition to a lack of energy, sleep deprivation is linked to a wide range of chronic health problems and can increase your risk of accidents that can lead to injury or death.

The reasons why aren’t entirely clear, but scientists have learned much about what happens during a night of good rest thanks to the work of UChicago scientist Nathaniel Kleitman, founder of the world’s first lab dedicated exclusively to sleep research. He and his team were the first to study how a person’s sleep patterns change over the course of a night, using electroencephalography (EEG) to track brain activity. The results showed that the brain becomes quieter and less active as you fall asleep, with electrical signaling falling into wave-like patterns that reflect different stages of sleep.

In the earliest phase of sleep, called delta waves, neurons in your brain send signals to your heart to slow down. As you enter the deeper stage of sleep, called REM, the neurons in your thalamus send images and sounds to the cerebral cortex, which processes these into your dreams. During REM, your dreams may be vivid and sometimes feel very real, but they aren’t stored in your long-term memory.

While you’re sleeping, the thalamus also sends and receives messages from the rest of your body, including the heart. This part of the brain also regulates stress hormones, such as cortisol, which helps keep your blood pressure and heart rate stable. Stressful events, whether it’s work or personal issues, can keep you awake at night and cause your heart to beat faster. This can lead to a higher risk of health conditions, such as heart disease. The best way to avoid this is to get a good night’s sleep and to relax before you go to bed. Maintaining a regular sleep schedule is important, as is staying away from caffeine and alcohol, exercising, and keeping your bedroom cool and dark.