The science of sleep has fascinated humans for centuries, but it’s still a relatively little-understood field. Prior to the 1920s, sleep was believed to be a truly “dormant” state in which the brain was passive.

 

But in 1924, a German psychiatrist pinpointed the fact that there were different patterns of wave activity occurring in sleeping versus awake test subjects. Rapid eye movement, or REM, was discovered about 30 years later. Since then, sleep researchers have made great strides, but still don’t fully agree on the purpose of REM sleep or all the mechanisms of sleep.

Here’s what we do know:

Types of Brain Waves

The different types of brain waves represent differing levels of activity during both wakefulness and sleep.

• Beta waves are the type of brain wave activity usually exhibited during wakefulness
• Alpha waves occur during relaxed states, such as meditation
• Theta waves occur during the first two stages of sleep
• Delta waves, the slowest, occur during the third and fourth stages of non-REM sleep

During REM sleep, a combination of all of these wave types, in addition to desynchronous waves, occur as we’re dreaming.

Sleep Stages and Brain Activity

Thanks to electroencephalography (EEG), scientists can “view” brain activity during various stages of sleep based on EEG waves. There are four non-REM, or slow-wave sleep stages, leading up to the REM stage — then the cycle starts all over again. This repeats several times throughout the night.

Non-REM stage 1 is the phase we enter when we first fall asleep. At this point, brain activity slows significantly. Correspondingly, the muscles relax and vital stats like heart rate and blood pressure drop.

In stage 2, the body prepares for deep sleep.

In stage 3, delta waves, which are long, slow waves of brain activity, are punctuated by occasional faster waves.

Stage 4 is a transitional period before REM sleep begins.

During non-REM sleep, memory consolidation and other cognitive functions take place. That’s why even short-term sleep deprivation can cause so many neurological issues.

What Happens During Dreaming?

During REM sleep, the dreaming stage, the brain becomes highly active–on par with brain activity that occurs when we’re awake–while the body is essentially paralyzed. A tiny section of the brain stem, the subcoeruleus nucleus, is in charge of REM sleep. In the rare cases that these specialized cells become damaged, sleepers’ muscles do not undergo paralysis, often causing the sleeper to physically “act out” their dreams.

While the biological purpose of REM sleep is not fully understood, evidence suggests that it is tied to emotional health. The brain is truly one of the last frontiers of science. The rapidly advancing field of sleep technology may soon change this most basic of biological functions, making science fiction a reality with innovations like “personalized optimization” for sleep on the horizon.

But for now, here’s to a good, old-fashioned eight-hour snoozefest!