✎ Written by: Denisa Cerna
✓ Fact-checked by: Kaija Sander, Ph.D.
“More than a third of adults in many developed nations fail to obtain the recommended seven to nine hours of nightly sleep,” says scientist and professor of neuroscience Matthew Walker, PhD, in the first chapter of his bestselling book Why We Sleep: Unlocking the Power of Sleep and Dreams.
This probably doesn’t come as a surprise. In many cultures, a lack of sufficient sleep is so common that a yawn coupled with “I’m so tired” hardly shocks anybody.
What may be of interest, however, is our “why.” Walker explains that our apathy toward sleep may be due to the fact we aren’t quite sure why we need it and what it does to us.
He offers an excellent metaphor: imagine the birth of your first child. The doctor congratulates you and tells you all looks good. Just before exiting, they add, “There’s just one thing. From this moment forth, and for the rest of your child’s life, he will repeatedly and routinely lapse into a state of apparent coma. It might even resemble death at times.
And while his body lies still his mind will often be filled with stunning, bizarre hallucinations. This state will consume one-third of his life and I have absolutely no idea why he’ll do it, or what it is for. Good luck!”
It might sound absurd when you put it that way. Mysterious, even.
Well, it’s time to look beyond the veil of sleep and discover why it’s so very important.
The Architecture of Sleep
Before we proceed any further, it’s vital that we understand how sleep works.
Broadly speaking, stages of sleep fall into two categories which continually repeat in approximately ninety-minute intervals: NREM sleep (non-rapid eye movement sleep, that is, deep sleep) and REM sleep (rapid eye movement sleep, that is, the stage when you have vivid dreams).
While we constantly go back and forth between NREM and REM during the night, the ratio changes as the night progresses.
In the first half, NREM sleep takes up the majority of our cycle. In the second half, the roles reverse. This is why most of our dreams take place in the early hours of the morning – it’s when REM sleep is at its most active.
Both stages are of extreme importance, which is why a full night’s sleep is needed in order to get a sufficient amount of both NREM and REM.
Why We Sleep: The Wonders of NREM Sleep
You might think that falling into deep sleep means you’re just lying in bed, oblivious to the world around you, doing absolutely nothing. Some people would even call it a waste of time.
This couldn’t be further from the truth, however. As Walker explains, NREM sleep plays a fundamental role when it comes to multiple different bodily functions, from memory consolidation to muscle repair, toxic waste clearance, and more.
As he so pointedly says, “Sleep is the single most effective thing we can do to reset our brain and body health each day – Mother Nature’s best effort yet at contra-death.”
Here are some of the findings explored in Why We Sleep that are based on Walker’s extensive research:
Learning and memory consolidation
When you learn new information, it gets stored in the hippocampus, which is a part of the brain that could be compared to a USB memory stick – it has a limited storage capacity.
When the capacity is exceeded, you may not be able to add more information or might mix up the information that’s already present. During Walker’s research, he contributed to the finding that it is during sleep that the information from the hippocampus transfers to a long-term storage site (in the cortex).
This means that sleeping before learning new information helps “clear” the hippocampus, allowing for better information retention once we wake up, and sleeping after learning helps consolidate that data in long-term stores of the brain. Therefore, it is, in fact, a great idea to have a good night’s sleep before an exam.
Extra Tip: Daytime naps of as little as twenty minutes can also help consolidate memories as long as they contain a sufficient amount of NREM sleep.
Motor skills improvement
Fact-based information isn’t the only thing NREM sleep helps us remember. Motor skills – such as playing a musical instrument or athletic performance – also benefit from it.
What’s more, insufficient sleep leads to reduced aerobic output, impairments in cardiovascular, metabolic, and respiratory capabilities, an increase in injury risk, and insufficient physical recovery from inflammation.
So, if you want your body to perform at its best, be it when running a marathon or playing the guitar at a concert, you should strive to enjoy plentiful sleep.
Nighttime power cleanse
When you enter deep NREM sleep, your brain rids itself of toxic waste via the glymphatic system.
While this system isn’t completely turned off during the day, its efficiency skyrockets during sleep. One of the toxins that are eliminated during this process is amyloid protein, which is associated with Alzheimer’s disease. In Walker’s words, “Sleep is neurological sanitation.”
Why We Sleep: The Marvels of REM Sleep
Your dreams may seem like an absurd mumbo-jumbo with no real significance, but according to Why We Sleep, REM sleep is actually incredibly important.
As Walker states, four main areas of the brain are found to be active during REM sleep:
The visuospatial regions at the back of the brain (related to visual perception)
The motor cortex (associated with movement)
The hippocampus and surrounding regions
The amygdala and the cingulate cortex, which are deep emotional centers of the brain that are up to 30 percent more active in REM sleep compared to when awake.
The prefrontal cortex, which is in charge of rational and logical thought (Walker calls it the CEO of the brain), is suppressed in activity during REM sleep. This is partly why REM sleep is such a hub of creativity.
But according to Walker’s book, that’s not the only reason why we dream…
Overnight therapy
When you dream about a stressful or emotionally distressing situation that has happened to you, you are more likely to make your peace with it on an emotional level and move on.
REM sleep, when most dreaming occurs, is the only time when the brain is free of noradrenaline, a molecule associated with anxiety. This absence allows the brain's emotional centers, which are highly active during REM sleep, to replay and process emotionally charged memories without the added stress.
Based on Walker’s research, REM sleep is “clearly needed in order for us to heal emotional wounds.”
Please note: This mechanism is more complex when it comes to people suffering from PTSD because their REM sleep tends to be disrupted due to excessively high levels of noradrenaline within the brain, blocking their ability to enter and maintain soothing REM sleep dreaming.
Problem-solving
In one of Walker’s studies, the participants worked on a problem before going to sleep and after having woken up.
When awoken from NREM sleep, they did not show significant improvements in creativity or problem-solving, but when awoken from REM sleep, their problem-solving abilities skyrocketed.
Solutions came to them more effortlessly, and their approach appeared more open-minded and fluid. This could be due to the fact that the logical part of the brain, the prefrontal cortex, is less active during REM, allowing thoughts and associations to flow more freely,fostering more creativity, open-mindedness, and imagination.
So, if you want to solve a specific problem, sleeping on it is, indeed, a good idea.
Emotional reading
A lack of sleep leads to higher emotional reactivity and poorer emotional self-regulation. This is partly due to the fact that REM sleep helps us tune into our emotions and read the facial expressions of the people around us when we’re awake in order to determine what they’re thinking or how they’re feeling.
Therefore, a lack of REM sleep makes us feel like we are viewing “an image through frosted glass,” as Walker says. Starving yourself of dreams makes it more difficult for you to decode other people’s emotions, making you give in to your fears and see even a friendly face as a potential threat.
The Effects of Sleep Deprivation
In Why We Sleep, Walker explains in great detail why sleep deprivation has catastrophic consequences and what we can do to prevent it.
Here is a non-exhaustive list of the effects of insufficient sleep:
Your ability to pay attention worsens, potentially leading to microsleeps which cause a great deal of car accidents
You have slower reaction times or stop responding altogether
You become more emotionally irrational and impulsive
You face a higher risk of developing Alzheimer’s disease
You’re at a greater risk of suffering a coronary heart disease, hypertension, and stroke
You are more likely to develop type 2 diabetes and gain weight
Your ability to reproduce may decrease due to a drop in important reproductive hormones
Your immune system isn’t as effective
There is a higher chance of cancer growth
Conclusion
Keep in mind that while many people think getting six hours per night is enough, Walker highlights that ten days of six hours of sleep causes the same impairment in performance as going without sleep for twenty-four hours straight.
Six hours is not enough. In order for sleep to fulfill its function, we need to get a sufficient amount of both NREM and REM sleep.
At the end of his book, Walker shares 12 steps for healthy sleep from NIH Medline Plus, including sticking to a regular sleep schedule, only napping before 3 PM, avoiding large meals late at night, and exercising no later than 2-3 hours before bedtime.
If you would like to learn more about sleep, Why We Sleep is the perfect choice. And if you’re in need of personal guidance, don’t hesitate to reach out to a mental health professional.
Myndlift provides a personalized expert-guided brain health program that can help you elevate your wellbeing by improving your sleep quality, focus, calm, and self-control over mood. Take this 10-second quiz to check if you’re eligible to kick-start your journey for better brain health.
About the author:
Denisa Cerna is a non-fiction and fiction writer who's passionate about psychology, mental health, and personal development. She's always on a quest to develop a better insight into the workings of the human mind, be it via reading psychology books or combing through research papers.
About the reviewer:
Kaija Sander is a cognitive neuroscientist and scientific consultant for Myndlift. She holds a BSc in Biomedical Science with a specialization in Neuroscience and Mental Health from Imperial College London and a PhD in Neuroscience from McGill University. Her doctoral research focused on brain connectivity relating to second language learning success. She is passionate about the broader applications of science to have a positive impact on people’s lives.
References:
NIH Medline Plus. Bethesda, MD: National library of Medicine (US). Tips for Getting a Good Night’s Sleep. 2012.
Walker, Matthew, PhD. Why We Sleep: Unlocking the Power of Sleep and Dreams. Scribner. 2017.