What Happens In Your Brain During The Two Critical Stages Of Sleep

We shouldn’t wear lack of sleep like a badge of honor. Our brains are actually doing important work to make us more successful as we snooze.

What Happens In Your Brain During The Two Critical Stages Of Sleep
[Photo: Flickr user Khánh Hmoong]

The average person spends one-third, or 36%, of their lives sleeping. That means if you live to be 90, you spend about 32 years asleep.


“What that 32 years is telling us is sleep, at some level, is important, and yet for most of us, we don’t give sleep a second thought,” says Russell Foster, a circadian neuroscientist, in his massively popular TED talk titled, “Why Do We Sleep?” “We throw it away. We just don’t think about sleep.”

Since sleep and its role in our lives is still mostly a mystery, those hours we rest are, unfortunately, thought of as a waste of time in our always-on, connected world. As the famous saying goes, “money never sleeps,” so those who can find a way to “cheat” sleep are accoladed for their “secret to success”—as if getting by on less sleep is accomplished through sheer determination.

But based on recent research, we know that a lot of things happen in our brain while we sleep. Below are further explanations of critical sleep cycles and how they affect our brain’s cell formations and ability to cleanse toxic proteins.

The Two Stages Of sleep

According to Vincent Walsh, a professor of human brain research and Royal Society industry research fellow at the Institute of Cognitive Neuroscience in London, people think the first half of sleep—the deep sleep stage—is most important because of how groggy they feel if woken up during this time. However, it’s actually the later part of REM sleep that’s more vital, because it’s necessary for the encoding of procedural memories, like knowing how to do things—walking, talking, or riding a bike.

Basically, the slow-wave deep sleep you have earlier in the night is necessary for explicit information, facts, new words, and encoding of declarative memories, like daily events or things you would learn in class, explains Walsh, whereas “REM sleep is for creative problem solving and motor skills.”

Additionally, REM sleep is also called paradoxical sleep because the body is paralysed.


“This is why you dream about flying and not being able to run and all of the bizarre stuff,” says Walsh, because your body is inhibited.

Why The Entire Night Is Critical

The information above shouldn’t encourage you to deem specific hours of sleep more important than others. In fact, we know that varying brain-wave states occur in 90-minute cycles where your brain is constantly establishing new memories and learning.

“One of the things that happens overnight is that brain cells that weren’t previously connected connect up with each other, and that allows more creative thinking,” says Tara Swart, a lecturer at MIT Sloan Executive Education and author of the book Neuroscience for Leadership. “There’s a lot of famous stories of people, just as they were falling asleep or just as they were waking up, having this moment of insight . . . something that you’ve been thinking about anyways. But it’s only when you’re only in a close sleep stage that you get a really good idea about it.”

As a result, Swart advises having a notebook next to your bed so you can jot down ideas or notes as you’re asleep or as soon as you wake up.


Additionally, humans need an uninterrupted six to eight hours of sleep to cleanse our brains overnight of neurotoxins, specifically harmful remnants like beta-amyloid, which are found in clumps in the brains of sufferers of Alzheimer’s disease. Without sleeping through this entire six- to eight-hour process, the brain’s cleansing system can’t filter bad proteins through your spinal cord. Even worse, the more beta-amyloid you have sitting in your brain, the less deep sleep you’re able to get, causing a vicious cycle and affecting the connections to take place in your slow-wave and REM sleep cycles.

Your Active Sleeping Brain

While our digital world seems to make it fashionable to be so busy and successful that you don’t have time to sleep, thinking this way assumes that your brain shuts down when you sleep. This is the opposite of what happens. In fact, our brains need the rest of our body to shut down so that it can work in overdrive.

The process is crucial for processing thoughts, memories, and forming new brain cells. Research even shows that some genes are turned on only when you sleep. Instead of thinking of sleep as a waste of time, we should be thinking of sleep as a time to open the door for greater cognitive abilities. And that’s the real secret to success.

Related: Are You Ruining Your Good Night’s Sleep?

About the author

Vivian Giang is a business writer of gender conversations, leadership, entrepreneurship, workplace psychology, and whatever else she finds interesting related to work and play. You can find her on Twitter at @vivian_giang.