The 4 Stages of Sleep and What Happens to Your Brain During Each

If you want to perform better in your daily life, improving your sleep is a great place to start. Throughout the night, your brain cycles through 4 different stages of sleep. There used to be 5 sleep stages, but the American Academy of Sleep Medicine changed the divisions in 2007. Each stage of sleep plays an essential role in keeping your mind and body strong.

There’s a reason you feel so refreshed after a good night’s sleep— it’s during the deeper sleep stages that your brain repairs and replenishes itself. Good sleep also regulates your mood, focus, creativity, and more.

Here’s an in-depth look at the 4 sleep stages, how each one changes your body and brain, and why it’s so important to spend time in all of them every night.

Why Is Sleep So Important?

When you’re awake, your brain is working hard. It uses about 20% of your daily calories, despite being only 2% of your body by weight.[1]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC124895/

But your brain can’t be running all the time. At some point it needs to power down and replenish itself.

That’s where sleep comes in. During sleep, your brain:

  • Refills energy stores to get ready for the next day
  • Cleans out cellular waste that built up while you were awake
  • Repairs damaged connections between brain cells
  • Encodes the day’s experiences into your memory
  • Stores knowledge and concepts that you’ve learned during the day

What happens if you don’t sleep?

Sleep is an important part of your daily cycle and is essential to brain function. But what happens if you don’t sleep?

Randy Gardner has the answer. In 1965, at the tender age of 17, Randy decided to stay up for as long as humanly possible.[2]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3057238/ He notified a Stanford University sleep expert, Dr. William Dement, who came to monitor him. The Navy was also interested; they sent one of their senior neurologists to observe the experiment.

With no caffeine or other stimulants, Randy stayed awake for 264 hours— just north of 11 days. He set a world record, but he also experienced a variety of (temporary) problems with his brain function, including:

  • Blurred vision
  • Trouble focusing
  • Loss of coordination
  • Slurred speech
  • Impaired memory
  • Trouble counting to ten
  • Persistent hallucinations and delusions (At one point, Randy— a 120-lb. high school boy— began to walk, talk, and act like he was football star Paul Lowe, the Super Bowl-winning halfback for the Los Angeles Chargers.)

It’s also worth noting that on day 10 without sleep, despite his considerable neurological deficits, Randy played two games of ping-pong with the Stanford doctor who was monitoring him— and Randy won both times.

Ping-pong skills aside, Randy’s case study reveals just how much your brain depends on sleep. It’s an indispensable part of your daily rhythm; without it, your body and mind deteriorate rapidly.

The 4 Stages of Sleep (and Why Each One Matters)

Every 90-120 minutes while you’re asleep, your brain cycles through 4 different sleep stages. Ideally, you want to spend a significant amount of time in the deeper stages every night, because each stage does something unique for your body and mind.

Let’s take a closer look at the 4 stages of a sleep cycle and why each one is important.

Stage 1 Sleep: Getting Ready to Rest

Stage 1 sleep is the shift from wakefulness to sleep. It typically only lasts 5-10 minutes, during which your brain activity begins to calm down and you begin to doze off.

During stage 1 sleep, you experience:[3]https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Understanding-Sleep

  • A shift from alpha brain waves (alertness and attention) to theta brain waves (relaxation and unfocused thoughts)
  • Lower heart rate
  • Decreased overall brain activity
  • Muscle relaxation
  • Slowed breathing

You may also experience myoclonic jerks during stage 1 sleep: the startling moments when your body twitches that can feel like you’re falling off a cliff. Myoclonic jerks are an occasional side effect of your brain function changing from an alert state to a resting state, and they happen to almost everyone at some point or another.[4]https://www.ncbi.nlm.nih.gov/books/NBK537015/

Stage 2 Sleep: Light Sleep for Learning and Memory

Stage 2 begins when you go beyond drowsiness and actually fall asleep. It’s still considered light sleep, but you experience a greater shift in body changes, including:

  • A drop in body temperature (down to around 95-96 degrees Fahrenheit)
  • Greater muscle relaxation
  • A steeper decrease in heart rate and breathing rate
  • Decreased awareness of your surroundings

You’re usually in stage 2 sleep for 10-60 minutes, depending on the sleep cycle you’re in. You move past stage 2 sleep quickly during your first sleep cycle of the night. But as time goes on, your brain no longer needs the restorative benefits of deeper stages, and you begin to spend the majority of your cycles in shallow stage 2 sleep.[5]https://www.ncbi.nlm.nih.gov/books/NBK19956/

Learning and Memory Consolidation

Despite overall slower brain function, your brain also produces short, rapid bursts of activity during stage 2 sleep. These bursts are called sleep spindles, and researchers believe that they help you break down and store memories from the previous day.[6]https://onlinelibrary.wiley.com/doi/10.1111/j.1365-2869.2012.01017.x People who focus on learning new information during the day see a significant increase in sleep spindles that night.[7]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6758170/

Sleep spindles may also make you harder to wake up by telling your brain to stop responding to stimuli in the world around you.[8]https://serval.unil.ch/en/notice/serval:BIB_082A1966C9A8

Stage 3 Sleep: Deep Sleep for Cleaning, Repair, and Creativity

During stage 3 sleep, you begin to produce delta brain waves: slow, steady waves of electrical activity in your brain. Delta waves are the main sign that your brain is in a state of deep, restorative sleep.[9]https://www.ncbi.nlm.nih.gov/books/NBK10996/ For this reason, stage 3 sleep is sometimes called “delta sleep” or “slow-wave sleep.”

Once you enter stage 3 sleep, your muscles relax completely. Your heart rate and breathing become very slow and almost perfectly regular, and you become quite difficult to wake up.

You typically stay in stage 3 sleep for 20-40 minutes, with more time at the beginning of the night and less time the longer you sleep.

Brain Cleaning

Stage 3 sleep activates your glymphatic system, which uses the fluid around your brain and spine to wash away cellular waste that builds up during the day.

Notably, your glymphatic system flushes out beta-amyloid plaques— bundles of proteins that seem to be a main cause of Alzheimer’s Disease—during deep sleep.[10]https://www.sciencedirect.com/science/article/pii/S2468867319301609.

Cellular Repair

During stage 3 sleep, you also begin to repair cellular damage from the previous day. You experience a large increase in human growth hormone (HGH),[11]​​https://www.ncbi.nlm.nih.gov/books/NBK19956/ which restores cells in both your body and brain, stimulates fat loss, and improves muscle power output.[12]https://pubmed.ncbi.nlm.nih.gov/20020365/

Creativity

Stage 3 sleep also stimulates creative thought. Studies show that people who get more stage 3 sleep experience increases in creative problem solving[13]https://pubmed.ncbi.nlm.nih.gov/21377416/ and insightful thought.[14]https://pubmed.ncbi.nlm.nih.gov/20195475/

Stage 4 Sleep: Dreaming and Mood

Stage 4 sleep, also called rapid eye movement (REM) sleep, is the deepest stage of sleep. You continue to experience slow, steady delta brainwaves during this stage, but your eyes also begin to dart rapidly back and forth in a random pattern.

Stage 4 sleep usually lasts from 10-60 minutes per sleep cycle, with more time in stage 4 for the first cycles of the night and less time in stage 4 as the night goes on.

Interestingly, you also see a rebound effect with this sleep stage. If you’ve been deprived of deep sleep for previous nights, you enter stage 4 sleep faster and stay there longer until you’ve made up the difference.[15]https://pubmed.ncbi.nlm.nih.gov/32809548/ The rebound effect suggests that stage 4 sleep is particularly important to your physiology— if you miss it, your body has a system in place to make up the difference.

Memory Formation

REM sleep is also when you dream, which researchers believe is the result of memory formation. The theory is that when you consolidate memory, your brain processes the various experiences and thoughts you’ve had recently.

The thoughts and experiences are varied, but your brain processes information in narrative (story) form, so it ties the different memories together to form a dream as it processes them.[16]https://pubmed.ncbi.nlm.nih.gov/24477388/

That explains why your dreams may be related to things you’ve experienced or thought about recently—and why they aren’t bound by the possibilities of the real world.

Mood and Mental Health

REM sleep also seems to be particularly important for mood and mental wellbeing. People who don’t get enough REM sleep see an increase in anxiety and depression. [17]https://pubmed.ncbi.nlm.nih.gov/30949927/

Improve Your Sleep, Improve Your Life

Sleep is a pillar of high performance. It affects almost everything you do: your mood, cognition, focus, physical ability, and more.

If you want to improve your sleep, nootropics are a great place to start. Take this quiz to get your personalized nootropic formula— a combination of supplements, cognitive enhancers, vitamins, and minerals that turn on your brain and help you do more with your days.

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