Deep sleep vs REM sleep: what each does, and how to get both

Deep sleep and REM sleep are two shifts of the same night. Deep sleep fills most of the first half and is linked to physical restoration and to saving the day's facts; REM, the stage of vivid dreams, takes over in the second half and works on emotions and on linking memories. Neither comes out ahead in the deep sleep vs REM sleep comparison, and the way to get more of both is the same: a full, regular night with both ends protected.

People often ask Matthew Walker how to get more deep sleep, or more REM. His first answer is a question of his own: why do you want more REM? They usually assume it's the good stuff (Huberman Lab). Walker founded the Center for Human Sleep Science at the University of California, Berkeley, and Gina Poe's lab at UCLA studies how specific sleep stages affect learning and memory (Huberman Lab).

Is low deep sleep on your tracker a problem?

If a tracker has told you your deep sleep is low, some context helps before you act on it. Deep sleep is greatest in young children and falls steadily with age, even when total sleep doesn't change (Harvard Medical School). Sleep psychologist Jade Wu calls having less of it in later life "normal, not a problem" (Jade Wu). Poe wears a tracker herself, but says the best are about 70% accurate at staging sleep, so "take it with a grain of salt" (Huberman Lab).

The number with an official target is total sleep: seven or more hours a night, on a regular basis, for adults aged 18 to 60, according to the American Academy of Sleep Medicine and the Sleep Research Society (Watson et al.). That is a better number to watch than any single stage.

If someone tells you that you snore loudly or gasp in your sleep, or you're often sleepy in the day despite enough time in bed, talk to a doctor (NHLBI).

How is a night of sleep built?

Sleep comes in two kinds, rapid eye movement (REM) and non-REM. Non-REM has three stages: stage 1 is the drift from waking into sleep, stage 2 is when you're properly asleep, and stage 3 is deep sleep, also called slow-wave sleep after the brain waves that mark it. The cycle repeats every 80 to 100 minutes, usually four to six times a night (NHLBI). The famous "90-minute cycle" is only an average. Walker says some people's cycles run shorter and others longer, though each person's length is fairly stable, and he calls products that promise to wake you at the end of a cycle "nonsense" (Huberman Lab).

What changes through the night is the mix. Early cycles hold most of the deep sleep, which shrinks in the second cycle and may vanish from later ones, while REM periods start short and grow longer towards morning (Harvard Medical School).

Stage 2 is usually called light sleep, but it takes up about half the night, and it's busy. It's when the brain produces sleep spindles, short bursts of electrical activity that help cement new learning, from a tennis serve to a set of verb endings (Jade Wu, Hello Sleep).

That shape is why the advice for both stages is the same: guard the start of the night for deep sleep and the end of it for REM.

Deep sleep vs REM: what does each one do?

Sources: NHLBI, Harvard Medical School's Division of Sleep Medicine, Jade Wu's Hello Sleep and the interviews cited in the text.

What deep sleep does

In deep sleep, Walker says, hundreds of thousands of brain cells fire together and fall silent together, producing waves several times bigger than those of the waking brain. The body follows, shifting into its calm, rest-and-digest mode (Huberman Lab), with heart rate and blood pressure falling (Harvard Medical School).

The first deep sleep of the night brings what Poe calls "a big bolus of growth hormone release," in men and women alike (Huberman Lab). It also works on memory. Sleep after learning is like hitting "the save button" on new memories, Walker says, and for fact-based memories it's deep non-REM sleep that does the strengthening (Huberman Lab).

What REM sleep does

REM is the stage of most vivid dreams, and your brain makes sure you don't act them out. "The brain paralyzes your body so your mind can dream safely," Walker says; on brain waves alone, he couldn't tell REM from waking (Huberman Lab).

Noradrenaline, the brain's version of adrenaline, slows during sleep, and in REM, Poe says, "it's the only time when it shuts off completely." In her view, that silence lets the brain weaken connections it no longer needs once the day's memories are written to long-term storage, like "erasing your thumb drive" (Huberman Lab). Walker has an image for the emotional side: REM strips the bitter rind of emotion off a memory and keeps the fruit. In his studies, the more REM people had, the more the emotional charge of a memory faded by the next day (Huberman Lab). REM also links ideas: people woken from REM in Walker's lab solved anagrams about 30% better than people woken from non-REM sleep (Huberman Lab).

Neither stage is the "good" one

Walker lists deep sleep's benefits and then warns against deciding it's the stage to chase.

"It turns out that they're all important. You need all of them." (Matthew Walker, Huberman Lab)

Asking how to maximize your REM, he says, is like asking how to maximize the yolk in your egg (The Peter Attia Drive). Wu puts it plainly: "a good night of sleep needs all the different types of sleep" (Hello Sleep).

How to get more deep sleep and REM sleep

You can't order one stage on its own. With a good sleep environment and habits, says Wu, "your brain will balance the different types of sleep for what you need" (Jade Wu). What you can do is stop cutting into either end of the night.

Protect the start: a steady bedtime and an early last coffee

Poe's case for a steady bedtime is hormonal. The growth hormone pulse of the first deep sleep is timed by your body clock, so if you go to bed a couple of hours late, "you might get some growth hormone release," but at a moment when your clock has already moved on. Asked whether that means consistent bedtimes as well as wake times, she answers, "Exactly." Fall asleep at 1 or 2 am, she adds, and early sleep is dominated by stage 2 rather than slow-wave sleep (Huberman Lab).

Caffeine thins deep sleep a little and total sleep more. A 2023 meta-analysis in healthy adults found that caffeine cut deep sleep by about 11 minutes and total sleep by 45; the authors judged the deep-sleep change too small to matter clinically on its own, unlike the loss of total sleep (Gardiner et al.). Our guide to how late is too late for coffee shows how to set a cut-off.

Protect the end: the morning is REM time

Walker gives an example. You normally sleep from midnight to 8 am, and one day you set the alarm for 6 to get a head start. You've lost 25% of your sleep, but because REM is packed into the end of the night, you may have lost 60, 70, maybe 80% of your REM (Huberman Lab). His cheapest way to get more REM runs the other way: sleep an extra 15 or 20 minutes at the end of the night, rather than going to bed earlier, and make it part of your regular schedule. Sleeping in by two or three hours at weekends shifts your clock, he warns, like flying from Los Angeles to New York and back (Huberman Lab). A fixed wake time keeps the extra minutes steady.

Alcohol cuts REM too. A 2025 meta-analysis found that about two standard drinks delayed REM and shortened it, and more alcohol made it worse (Gardiner et al.). As the alcohol wears off, REM rebounds, but awakenings become more frequent (Harvard Medical School). Our guide to alcohol and sleep goes drink by drink.

The 1h Protocol for Better Sleep looks at the whole night the same way: the protocol it builds lays your evening and morning out on one timeline, from your last coffee to your get-up time.

So, why do you want more REM?

Walker's question is a fair one to put to any tracker score. Deep sleep works early, REM works late, light sleep runs through both, and the brain adjusts the mix to the day you've had. What helps sits at the edges of the night: a bedtime your body clock can count on, caffeine early, no nightcap, and an alarm that leaves the last hours alone.

"Sleep for as much as you possibly can sleep." (Matthew Walker, Huberman Lab)

Which end of your night is getting cut short? The free part of the 1h Protocol for Better Sleep asks about your evenings and nights and gives you one first step. Start free.

Frequently asked questions

Is deep sleep or REM more important?

Neither. Deep sleep, mostly early in the night, is linked to physical restoration and saving new facts; REM, mostly late, to emotional processing and connecting memories. Matthew Walker's answer is that "they're all important. You need all of them" (Huberman Lab).

How much deep sleep do you need?

There is no official target for deep sleep. A healthy adult typically spends about 15 to 20% of the night in it, less after middle age (Hello Sleep). The guideline that exists covers total sleep: seven or more hours a night for adults aged 18 to 60 (Watson et al.).

How do I get more deep sleep?

Keep a regular bedtime, keep caffeine well away from it and give yourself enough time in bed (Huberman Lab; Gardiner et al.). After short or broken nights, the brain lengthens and deepens slow-wave sleep by itself (Harvard Medical School).

Why do we dream in REM sleep?

Nobody fully knows. Harvard's sleep medicine division says the reasons we dream "still largely remain a mystery," and that REM's waking-like brain activity probably explains why its dreams are so intense. Some dreaming happens in other stages too (Harvard Medical School).

What is the difference between deep sleep and light sleep?

Light sleep (stage 2) fills about half the night and produces sleep spindles linked to learning. Deep sleep (stage 3) takes about a sixth of the night and is marked by big, slow brain waves (Hello Sleep). It's also harder to wake from: people roused from it are often confused and fall back asleep easily, Gina Poe notes (Huberman Lab).

Sources

This article draws on Matthew Walker's and Gina Poe's interviews on Huberman Lab, Walker's conversation with Peter Attia, Jade Wu's book and the public-health pages and research listed below. It is education, not medical advice.

• Huberman Lab Guest Series with Matthew Walker, Ep. 1: The biology of sleep and your unique sleep needs (podcast episode, 2024)
• Huberman Lab: Use sleep to enhance learning, memory and emotional state, with Gina Poe (podcast episode, 2023)
• Huberman Lab Guest Series with Matthew Walker, Ep. 4: Using sleep to improve learning, creativity and memory (podcast episode, 2024)
• Huberman Lab Guest Series with Matthew Walker, Ep. 5: Improve sleep to boost mood and emotional regulation (podcast episode, 2024)
• The Peter Attia Drive #47: Matthew Walker on sleep, Part 1 of 3 (podcast episode)
• NHLBI: How sleep works, sleep phases and stages (US National Institutes of Health public guidance, 2022)
• Harvard Medical School, Division of Sleep Medicine: What is sleep? (public education, 2021)
• Jade Wu, Hello Sleep (book, publisher's chapter 1 excerpt, 2023)
• Jade Wu: Sleep questions and answers (sleep psychologist's FAQ page)
• Gardiner et al., The effect of caffeine on subsequent sleep (systematic review and meta-analysis, Sleep Medicine Reviews, 2023)
• Gardiner et al., The effect of alcohol on subsequent sleep in healthy adults (systematic review and meta-analysis, Sleep Medicine Reviews, 2025)
• Watson et al., Recommended amount of sleep for a healthy adult (AASM and Sleep Research Society consensus statement, 2015)
• NHLBI: Sleep apnea symptoms (US National Institutes of Health public guidance, 2025)