Why We Sleep: What Really Happens When We Sleep?

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Last week I released part 1 in a series called Why We Sleep that will run through this week and into next week. Today we’ll cover what happens when we sleep and discuss some misconceptions, and next Wednesday, we’ll wrap up with a complete list of awesome sleep hygiene tips I know you’ll find super helpful. 

When I discussed the health risks of insufficient sleep in the first installment of Why We Sleep, I didn’t share much about the how or the why these health risks arise. A big part of how and why things start to go awry when we skip out on the zz’s is tucked into the answer to this question: “what happens when we sleep?” What actually takes place in our brains when we check out for the night is quite extraordinary. You might be surprised to find out that it’s only when we sleep that certain processes occur, and there’s no getting around it. 

why we sleep, what happens when we sleep?photo on the left side of this image taken by Mike Durkin, cropped and color balance altered, sourced through Creative Commons

What Happens When We Sleep?

A Symphony of Synchrony

Matt Walker’s research at UC Berkeley’s Sleep and Neuroimaging lab revealed what he calls a symphony of brain activity. In our deepest stages of sleep (stages 3 and 4), brain cells all fire together and then become silent. Hundreds of thousands of cells all unite to do the exact same thing, creating this mass synchrony effect. While this is happening, the cortex goes into a default mode of a slow but highly synchronized chant.

That’s all fine and good, but so what? What does this do for us day to day?

When large parts of the brain start syncing up, the brain is able to connect different pieces of information across vast distances, precipitating the synthesis of complex ideas and experiences and creating a “rich tapestry” of knowledge and information across the span of the entire brain. It takes what we learned that day and connects it to stored information, creating context, relationships with information new and old, and a deeper understanding of complex ideas. Matt Walker described it as “converting knowledge to wisdom.” I love that. Don’t you? 

Waste Management Services

I came across a video that explains how sleep serves as a waste removal system, flushing toxins from the brain, including beta amyloid, which is implicated in Alzheimer’s disease. They do a great job of explaining it, so I’ll just let them do that. Check it out.

Our Memory Maker

Think of the brain like a sponge with a bucket underneath it, and all day long (in waking life) the sponge gets filled with the water of what we take in (information). Now think of the night (while we’re sleeping) as the time to wring out the sponge and store the liquid in the bucket underneath to make room for the next day’s water supply. This wringing out takes place in Stage 2 non-REM sleep and at no other point in our sleeping or waking lives. Without it, we simply can’t continue to take in and retain new information.

The effect of missing out on vital sleep is two-fold:

1. If we miss a lot of sleep the night BEFORE we take in important information, our chances of making solid memories of what we learned are greatly diminished, as our sponge is too full to hold onto much of anything new.

2. If we miss a lot of sleep the night AFTER we take in this information, the memories won’t be wrung out — they won’t be cemented into the architecture of the brain (stages 3 and 4 of non-REM sleep).

As Walker says, “If you don’t snooze, you lose.” I guess I wasted a lot of energy pulling all-nighters before big tests in college … 

Our Weight Watcher

Research has shown that insufficient sleep results not only in insulin resistance, but also an increase in ghrelin and a decrease in leptin. What are all these words??

Insulin resistance is a precursor to diabetes and is one of the main features of metabolic syndrome. It takes place when cells don’t properly take in insulin to neutralize glucose. This means higher levels of blood glucose upon waking — so high in fact, that you could get a positive reading for prediabetes after just a few nights of short sleep. Free-flowing insulin in the blood stream also has the potential to damage organs like the brain, kidneys, and liver. why we sleep, what happens when we sleep?

Ghrelin and leptin are the hormones that tell you when you’re hungry and full, respectively. When you don’t get enough sleep, chances are these hormone are telling you that you’re not full, and to keep on eating. Additionally, when we’re tired we tend to go for the sugary or starchy foods first, to give us a jolt of energy to get through the day. As you might have already noticed, this is the start of a vicious cycle that can result in weight gain and diabetes.

Full-blown Type 2 Diabetes comes with its own sleep challenges as well. Diabetics are more likely to have sleep apnea and damaged/inefficient kidneys, both of which can wake them up intermittently throughout the night (to breathe and to use the bathroom), exacerbating an already troubling problem. 

You can learn more about the connection between sleep and these hormones (and therefore weight) in my post Why Gut Health Matters: Your Weight. That post is part of a series too. If you haven’t checked it out, I suggest you bookmark it!

Our Alarm System

Fascinating research (also by Matt Walker and the folks at UC Berkeley) has determined that poor sleep creates a misfire when it comes to detecting facial expressions and the intentions of those around us. In other words, super sleepy people can’t tell if someone is a friend or a foe, if someone intends to shake their hand or do them harm. The distress signal from the brain to the heart is disconnected. “Sleep deprivation appears to dislocate the body from the brain,” said Walker. “You can’t follow your heart.” 

We lose our innate self-protective mechanisms when we lose sleep. We might also lose a fight with our partner when we misread their intention to give us a hug as their intention to tease us. 

Misconceptions About Sleep

Think you’ve found some short-cuts to get around short-sleeping yourself? Think again! I’ve compiled the 3 most common misconceptions about sleep and explained the science behind their inaccuracies. Get ready for some debunking!

1. As we get older, we need less sleep.

Older people can’t generate sleep as sufficiently, but they do in fact need just as much, if not more sleep than young to middle-aged adults. Evidence shows that as you age, some parts of the brain deteriorate more quickly than others, and unfortunately those that generate sleep atrophy more quickly than other parts of the brain. If you’re getting older and noticing that you’re having trouble falling or staying asleep, seek help from a sleep professional.

why we sleep, what happens when we sleep?

2. You can acclimate to sleeping less, and eventually just need less sleep.

Habituation doesn’t change in terms of the body’s needs to function optimally. Your subjective sense of how well you’re doing on very few hours of sleep is not a good predictor of your objective state of alertness and functionality. You don’t know the consequences of sleep deprivation when you’re sleep deprived, just as someone who’s had a few drinks can’t quite tell that they probably shouldn’t get behind the wheel. This analogy is especially disturbing, because it’s been convincingly demonstrated that driving while exhausted is frighteningly more dangerous than driving while tipsy.

Human beings are the only species that deliberately deprive themselves of sleep. No other organism does this. There’s no evolutionary strategy to help us overcome sleep deprivation. 

3. If you need to stay up during the week, you can make it up on the weekend.

You can’t pay off your week’s sleep debt by binge sleeping on the weekends. Walker calls this one “sleep bulimia,” because it’s a binge/purge situation. The truth is, your brain never makes back up all the sleep it lost on the night of deprivation. Sleep allows us to sufficiently store the day’s information, so when we deprive ourselves within the first 24 hours of learning something new, we are far less able to store it for later use. Recovery sleep does not resolve this problem unless we relearn the information and sleep adequately immediately following (within 24 hours).

Today’s Action Item

I hope this information didn’t PUT you to sleep, but MOTIVATED you to take the necessary measures to strive for deep, restorative, consistent sleep. Last week, I shared one of the top 10 tips for getting a great night’s sleep:

Sleep Tip #1: Your bedroom is only for sleeping (and sex). Train your brain to associate your bed with sleeping and eliminate anything that could create racing thoughts or non-sleep in the bedroom.

This week, I’ll share the second tip for you to work on between now and next time when I’ll share the whole list. 

why we sleep, what happens when we sleep?


If you missed part 1 of this series: 8 Reasons to get 8 Hours, go check it out!

Sources for today’s post:

Inquiring Minds Podcast with Matt Walker: Why Did We Evolve to Sleep





I'm a wellness professional with a Master's in Integrative Health, passionate about spreading health, happiness and personal fulfillment to as many people as possible. I have a professional background in health and wellness, dietary supplements, and nutrition, and embark every day to live a well, balanced, happy life. In being true to myself and what I seek in life, I hope to inspire others to do the same, to cultivate wellbeing in their own lives.

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