We're going to uncover what sleep is and explore the stages of sleep and the corresponding electrical activity in the brain.
We will then dive into the intricacies of the neurobiology of sleep, what sleep does, what sleep deprivation leads to, and finally, what you can do to improve your sleep.
Sleep is an essential part of life. Sleeping an average of eight hours per night means we spend a third of our lives sleeping.
We use to think of sleep as a passive process, but it turns out that your brain is actually extremely active during sleep.
On average, healthy adults need about seven and a half to eight hours of sleep to feel functional. Some people need more, like pregnant women, for instance, and some people require less than eight hours, but these are usually the exceptions to the rule.
Throughout life, our sleep needs change. If you consider infants, for example, it seems they sleep all the time, that's because infants needs about 16 to 20 hours of sleep a day. By the time they're toddlers, that need decreases to about 12 to 14 hours and teens needs about 10 hours per day.
Let's look at normal sleep physiology. A normal sleep night is made up of five stages, Stages 1 through 4 or what is called Non-REM Sleep and REM sleep or Rapid Eye Movement Sleep. During non-REM sleep, many of the restorative functions of sleep occur. Whereas REM sleep allows for memories and thoughts from the day to be processed.
Sleep stages progress cyclically from 1 through 4, then onto REM and then they restart back at Stage 1. One complete cycle takes about 90 to 110 minutes. First cycles have relatively short REM sleeps and as the night goes on, REM sleep increases.
You cycle mostly between Stage 2 and REM.
In Stage 1, you can feel yourself drifting in and out. During this stage, there are slow roving eye movements.
In Stage 2, those eye movements stop and the overall brain activity slows down a bit. It's characterized by special wave forms called spindles that have been found to be abnormal in certain psychiatric diseases.
Stages 3 and 4 are called slow wave sleep. This is also called deep sleep because it's difficult to wake a person in this
state. It's also the stage when some people with perisomnias or sleep disorders sleepwalk or have night terrors.
REM sleep, on the other hand, makes up about 20% of your sleep. This stage use to be called paradoxical sleep because here your heart rate, and breathing increase, and your eyes start moving rapidly, hence rapid eye movement name.
In this stage, it looks like someone is awake, but the muscles are actually paralyzed. If you have ever had an episode of sleep paralysis where you wake up and can't move, you probably were in REM sleep. It's also the stage of sleep where dreams occur.
As we age, our sleep needs change. Not only the number of hours needed to function well, but also the quality of sleep.
The elderly, for example, get a lot less REM sleep and their sleep is much more fragmented as it cycles between awake and REM stage sleep often. They also don't get nearly as much slow wave sleep or deep sleep as a young adult.
So, what is the biology that controls these seemingly well orchestrated sleep cycles?
Let's explore that next.