Is REM Sleep Good For You? The Surprising Answer

This article is an excerpt from the Shortform summary of "Why We Sleep" by Matthew Walker. Shortform has the world's best summaries of books you should be reading.

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Is REM sleep good for you? Why is REM sleep good?

When you ask is REM sleep good for you, it’s important to think about the entirety of the human sleep cycle. REM sleep serves a certain purpose, and has specific effects on the human brain. So is REM sleep good for you? Let’s find out.

How Sleep Cycles Change Through the Night

Notice that not all sleep cycles look the same. As the sleep progresses through the night, a greater fraction of each cycle is spent in REM sleep. But is REM sleep good for you?

Why would the sleep cycles be unbalanced in this way? Why not just have all sleep cycles look the same, with 80% in NREM and 20% in REM, especially if we know the answer to the question is REM sleep good sleep.

The author hypothesizes that it’s like making a sculpture out of a mass of clay. Earlier in the night, more NREM is needed to clear out junk memories that aren’t useful anymore. Then once only the useful stuff remains, REM strengthens what’s left. This helps answer the question is REM sleep good for you.

(Shortform note: One way to think about this is that an animal might be interrupted in the middle of the night. So if an animal could only sleep 3 hours in one night, it’d make sense for the more critical functions to be performed first, with the later functions being a luxury if the animal could sleep a full night. This may suggest that NREM performs a more vital function for survival.)

Also beware of what this means for cutting your sleep short. If you normally sleep 8 hours, and one night you have to cut sleep to 6 hours, then you’re not just losing 25% of sleep – you might be losing 60-90% of your REM sleep! 

Likewise, going to sleep later than usual might cut short your NREM sleep.

Is REM Sleep Good For You? What REM and NREM Look Like

Is REM good sleep compared to NREM? REM and NREM are distinguishable by measuring electrical activity in the brain. NREM is characterized by slow (3-4 Hz) waves that propagate far from the frontal cortex to the back of the brain. REM is characterized by faster (30-40 Hz), frenetic activity that looks the same as being awake.

Wakeful thought looks frenetic because many different neural signals are occurring at once throughout the brain. An analogy: it’s like a microphone picking up a football stadium full of distinct conversations. The summation of all the conversations just looks like noise.

In contrast, NREM sleep is a slow, pulsing wave that’s noticeably different from REM sleep. So is REM good sleep? Continuing the analogy, it’s like a stadium full of voices singing in synchronization. That billions of neurons can do this together is awe-inspiring.

What’s the function of these slow NREM waves? By being lower frequency, slow NREM waves can propagate further without attenuation, like AM radio waves. The author suggests this is useful in transferring memories far across the brain, from temporary memory stores toward more permanent storage. It also allows communication across the brain for different sections to collaborate on their shared experience.

REM sleep looks like awake activity, and it’s where dreams happen. A few odd things happen during REM sleep:

  • Your sense of time in dreams seems dilated – an hour may seem to pass when in reality only 5 minutes have.
  • Unlike the rest of sleep, you consciously perceive your senses, like sight and sound. In non-REM sleep, the thalamus in your brain blocks you from consciously perceiving senses. Once REM sleep starts, this blockade is released.
  • In REM sleep, your eyes move rapidly This was initially thought to be visual exploration of the dream field, but this turns out to be more related to the creation of REM sleep than passive observation of it.

If REM sleep looks like wakefulness, how can an observer distinguish someone who’s dreaming from being awake? And how do you know the answer to is REM sleep good for you. Muscle atonia – during REM sleep, your voluntary muscles are completely limp. Your brain does this to prevent you from acting out your dreams, since fighting an enemy might cause you to accidentally punch your surroundings.

One last detail: sleep spindles (bursts of activity) occur at the end of slow waves, possibly serving a function to block external sensory input from disrupting sleep. People with more sleep spindles are heavier sleepers. This can help you understand the idea of is REM good sleep.

Is REM sleep good for you? Not only is REM sleep good for you, but it’s an essential function of both your body and brain.

Is REM Sleep Good For You? The Surprising Answer

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Like what you just read? Read the rest of the world's best summary of Matthew Walker's "Why We Sleep" at Shortform .

Here's what you'll find in our full Why We Sleep summary :

  • Why you need way more sleep than you're currently getting
  • How your brain rejuvenates itself during sleep, and why nothing can substitute for sleep
  • The 11-item checklist to get more restful sleep today

Carrie Cabral

Carrie has been reading and writing for as long as she can remember, and has always been open to reading anything put in front of her. She wrote her first short story at the age of six, about a lost dog who meets animal friends on his journey home. Surprisingly, it was never picked up by any major publishers, but did spark her passion for books. Carrie worked in book publishing for several years before getting an MFA in Creative Writing. She especially loves literary fiction, historical fiction, and social, cultural, and historical nonfiction that gets into the weeds of daily life.

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