It's rare to read an article, study, or how-to on sleep that doesn't mention these three letters in particular: REM. Whether in music ("Losing My Religion," anyone?), film (Inception was a major hit centered around the precious hours of REM), media, or academia, REM (rapid eye movement) sleep is touted as the sleep standard to strive for each night. Between its function to enable dreams and process important motion based memory (also known as procedural memory), you've likely heard of REM sleep's impressive resume of wellness-enhancing abilities.
Brace yourself, though -- contrary to just about everything you've heard about sleep science, there's more to a good night's sleep than just your hours of REM. Another, more intense layer of sleep precedes REM for most people, and it's called "deep sleep." While it might sound like a made-up phenomenon created by hypnotists or meditation coaches, deep sleep is actually an essential part of a typical night's sleep cycle that falls between light sleep and REM.
So what exactly does this lesser-known phase of sleep do for your body? A lot, as it turns out, that you can't live without. Here's what you need to know about your brain on deep sleep.
1. Deep sleep energizes the brain -- and your body.
You might not realize it, but when you're asleep, your brain actually stays awake -- in a way. While your body is at rest, your brain waves continue oscillating, slowing down and speeding up based on what hour you're at in your sleep cycle. During REM sleep, your brain waves look similar to when you're awake, with neurons firing in all directions creating steep, jagged brain waves. Deep sleep, on the other hand, causes brain activity to slow down significantly and is characterized by synchronized, steady oscillations of brain waves at a lower frequency of rhythm.
So what does this mean? A 2010 study on sleep and energy levels tells us that, during these slow oscillations of deep sleep, the production of the body's energy molecule ATP surged -- meaning that it is in fact deep sleep that creates energy for the next day. Next time you're jonesing for that second cup of coffee in the morning, remember this.
2. Toxins and waste are removed.
It sounds strange, but your brain gets littered with toxins and waste throughout the day. Turns out, your night's sleep helps keep your brain clean and healthy too, by using cerebrospinal fluid (CSF) to flush out the waste collected during the day.
This handy process does double duty, though. This same CSF also attacks and washes away a toxic protein called beta-amyloid, often found in large quantities in the brains of Alzheimer's patients. Keeping beta-amyloid from collecting in the brain is one of deep sleep's essential responsibilities.
3. It consolidates your memories.
It's not a secret that your day's events -- however big or small they may be -- are turned into actual memories overnight. We all learned this lesson in basic science classes long ago, but this process is actually entirely in the hands of deep sleep. According to a different 2016 report studying sleep and memory, these same slow oscillations characteristic of deep sleep also indicate that the hippocampus (which stores your recently acquired memories) and the cortex (where long term memories are housed) are likely to be communicating with each other directly -- solidifying the memory-making process every night.
Deep sleep is responsible for the formation of declarative memories specifically, which constitute those that you can verbally describe rather than skills-based ones. Thanks to deep sleep, you'll always remember what happened on Game of Thrones last night or what you ate for lunch yesterday -- whereas during REM sleep, procedural memories like learning how to ski are collected.
4. Deep sleep keeps your body growing.
Deep sleep's last major function lies in hormone release. From youth to old age, while you sleep, your brain releases essential developmental hormones, like growth hormones and those utilized during glucose metabolism. It stands to reason, then, that chronic diseases like obesity and high blood pressure are more common among sleep-deprived people. It's also not surprising, then, that the amount of deep sleep you receive decreases as you age -- you're not growing anymore, so your body doesn't need as much time to release those growth hormones.
So how can you make sure you're taking advantage of deep sleep?
Of course, sleeping pills and herbal solutions are often advertised as giving your body better sleep -- those containing the molecules gaboxadol and tiagabine -- but a wealth of dependence-related and negative side effects could be a risk. Even gamma-hydroxybutrate (GHB as it's abbreviated), the only drug on the market that actually gives you more hours of sleep, is better known as a date rape drug. Also proven effective are electric and magnetic stimuli in the brain, but we don't all have that kind of technology lying around.
Instead, try going a more natural route. Sound -- and most importantly the timing of its release -- can help you optimize your sleep for better performance and rest. While many of us prefer silence when we sleep, noise at the right frequency (that creates sustained and slow oscillations of sound) can stimulate the brain to induce deep sleep. It might sound a little sci-fi, but trust me -- your body and your brain will thank you tomorrow morning.