Do Sleep Stages Matter? How EEG Insights Can Improve Your Rest

Sleep might seem straightforward on the surface: Close your eyes, drift off for seven to eight hours, and wake feeling refreshed. But research over the last century has shown that sleep is a complex process during which our brain is very active. 

Every night, we move through the four stages of sleep, repeating in recurring cycles. The duration and quality of each of the sleep stages impacts how rested and refreshed we feel when we wake up.

Here, we’ll explain the science of sleep stages and how you can better tune into the process to ensure you get the best possible sleep.

Quick history: How EEG helped identify the sleep stages

In the 1920s, German psychiatrist Hans Berger recorded the first human electroencephalogram (EEG), a technique that measures electrical signals in the brain. Thirty years later in the 1950s, EEG became widely used to study sleep and revealed that, rather than one singular experience, our brain waves move through different patterns — or “stages” — throughout a night’s sleep. 

From this, researchers identified that sleep could be divided into two main stages based on the unique EEG signals: non-rapid eye movement (NREM) and rapid eye movement (REM). 

Today, EEG studies are foundational to sleep science, allowing clinicians to look into how each sleep stage influences our biological functions and contributes to physical and mental recovery.

What is the sleep cycle?

The sleep cycle is a period of brain activity that lasts roughly 90 to 110 minutes and repeats four to six times per night. Throughout the night, your body cycles through three different stages of NREM and then one stage of REM sleep multiple times. Each stage is crucial for a different set of cognitive and physiological functions, such as repairing cells, processing memories, and regulating emotions.

Breakdown of the sleep cycles and their typical duration

Each sleep stage has distinct neurological characteristics and lasts for a specific duration. Certain factors, such as depression, getting older, medications, or a traumatic brain injury can alter how much time you spend in each sleep stage. But for most healthy adults, your nightly sleep cycle looks like this:

Sequence of the sleep stages

Whenever you sleep (with the exception of cat naps), your brain cycles through each sleep stage multiple times. You progress from light NREM sleep (N1) to deeper NREM sleep (N2 and N3), ending with REM sleep before the whole thing starts over. 

As the night goes on, your N3 stage gets shorter, while REM grows longer, until eventually you reach a Wake/Alert stage in the morning.

Overall, we spend on average:

• 5 percent of total sleep time in light (N1) sleep
• 45 percent in N2 sleep
• 25 percent in N3 deep sleep
• 25 percent in REM sleep

Why do the sleep stages matter?

Each stage of sleep serves a vital purpose, influencing how we feel, think, and function. NREM sleep, particularly N3 deep sleep, is associated with growth hormone release, tissue repair, and immune function, making it especially restorative to our physiology. Meanwhile, REM sleep is crucial for memory processing and emotional health, helping to integrate daytime learning and manage stress. 

As you may have guessed, not spending enough time in each stage of sleep impairs your body and brain’s ability to function at 100 percent. Research suggests sleep deprivation is linked to a compromised immune system and higher inflammation, and that people who spend less time in REM sleep, in particular, perform worse on executive function tests (how well you interpret and react to information).

That said, the amount of time each person spends in each phase varies. While tracking sleep data can help you understand general patterns, you shouldn’t stress too much about the distribution of your sleep time among each stage. Minor variations are totally normal, and focusing too heavily on your breakdown can spike anxiety, which can create its own set of sleep issues. What matters most is that you’re getting a high-quality, full night’s rest.

The Tone Take: Each stage of sleep has important benefits

Though sleep seems simple, it’s an intricate process, with four different sleep stages, each offering unique benefits for the body and mind. Understanding how sleep cycles work can help you prioritize good sleep hygiene habits, like maintaining a consistent bedtime, managing stress, and creating a calming environment. These practices, in turn, enable your body to receive the full restorative benefits of each sleep stage, contributing to your long-term health and well-being.