Today, we’ll learn about the four different stages of sleep. When you sleep, your body goes through a few distinct phases, and each phase does different things to your brain and your body. If you miss specific phases, you miss out on their unique benefits. So what exactly happens in each of the four stages of sleep?
Stage 1 is that hazy hypnotic phase between being awake and being full-on asleep. As you enter stage 1, everything in your mind and body begins to slow; the randomness of your brain activity starts to synchronize, and the neurons start to fire across your brain in increasing unity. The temperature near your skin drops. Your heart rate and metabolism slow. And often, you experience little involuntary shockwaves, called myoclonic jerks, which can make you feel like you’re falling (sometimes waking you up), but more often sending you deeper into sleep.
During stage 2, your brain starts sending out little signals known as sleep spindles. Spindles help sort through your newly learned memories so they stick. For instance, if you spent the day working on your golf swing, your spindles help you develop the muscle memory for reuse on your next outing.
Slow Wave Sleep
Then your brain slows even more and your blood vessels constrict as you enter the deep dark world of slow wave sleep. The blood vessels constrict, and you enter into the deep dark world of stage 3, also known as slow wave sleep. It’s named for the notable increase in the slow delta wave that shows up on the EEG.
During slow wave sleep, it will take a loud bang or a sound of particular relevance, like your name or the cry of your baby, to pull you out of its deep trance.
Slow wave sleep is an essential period of repair. All the physical benefits of sleep occur now—primarily hormonal changes that bring your tissue and organs back to peak levels and help you metabolize fat and carbs. Slow wave sleep also clears your mind. During the day, you take in a lot of information that can burn out your brain cells and lead to fatigue-related errors.
Your brain then emerges from slow wave sleep and finds itself back in stage 2. But after about eight minutes of stage 2, everything changes. Your slow breathing becomes less regular. Your heart rate, body temperature, and blood pressure all start to fluctuate. And your neurons, previously firing in a slow rhythm, speed up and resemble the same random pattern as wakefulness. Your eyes dart back and forth beneath your eyelids. This period of rapid eye movement is when you experience vivid dreams.
Rapid Eye Movement (REM)
During REM, your brain emits neurotransmitters that are essential to learning and memory. This stage is especially important in helping cultivate higher-order cognitive skills, like finding patterns in complex information or coming up with creative solutions to difficult problems. Without REM sleep, eureka moments are fewer and farther between, but with it, the brain might experience true breakthroughs.
These stages define our cycle of sleep. In the next lesson, we’ll talk about sleep inhibitors that can prevent you from getting the rest you need.
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