Sleep is divided into two main types: non-REM sleep and REM sleep, with different stages serving different functions for the brain and body at different times in the night.
Understanding the structure of sleep is crucial for optimizing sleep quality and ensuring the obtaining of all stages of sleep for optimal rest.
Deep dives
The Structure of Sleep
Sleep is divided into two main types: non-rapid eye movement (non-REM) sleep and rapid eye movement (REM) sleep. Non-REM sleep is further divided into four stages, with stages 1 and 2 being lighter sleep and stages 3 and 4 being deeper sleep. REM sleep, characterized by dreaming, is the stage in which most vivid dreams occur. Throughout the night, the brain cycles through these stages every 90 minutes, with the balance of non-REM and REM sleep changing as the night progresses.
Brain Activity During Sleep
During deep non-REM sleep, the brain generates powerful, slow brain waves that flow over the cortex. Sleep spindles, short bursts of electrical activity, also occur during non-REM sleep. After about 60 or 70 minutes, the brain begins to rise back to lighter stages of non-REM sleep and then enters a short period of REM sleep. This cycle repeats every 90 minutes throughout the night, with the ratio of non-REM to REM sleep changing as the night progresses.
Understanding Sleep Structure for Optimal Sleep
Understanding the structure of sleep is important in optimizing sleep quality. Different stages of sleep serve different functions for the brain and body at different times in the night. Disrupting the later part of the sleep cycle, where most REM sleep occurs, can significantly impact the amount of REM sleep obtained, which is crucial for various cognitive processes. By understanding sleep structure, individuals can design personalized sleep schedules to ensure they obtain all stages of sleep for optimal rest.
Human sleep has been separated into two main types: Non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep
NREM sleep is further divided into four stages, with each stage increasing in their depth of sleep
REM sleep is named this way because of the bizarre, horizontal, shuttling eye movements that occur underneath your eyelids during this stage of sleep
REM sleep is the principal stage in which we dream, although it can occur in the other stages as well
NREM and REM sleep play out in a battle for brain domination throughout the night
This cerebral war is going to be won and lost every 90 minutes, creating the standard cycling architecture of sleep for humans
Other species may have a slightly different NREM to REM cycles, with birds experiencing a cycle that only lasts about 4-5 minutes, and giraffes about 24 minutes
During NREM sleep, we see bursts of deeply powerful brain waves that flow over your cortex
We also see sleep spindles, which are short, synchronous bursts of electrical brain wave activity that last for about 1-1.5 seconds
About 60-70 minutes into your first sleep cycle, your brain starts to rise up again into later stages of NREM sleep, then pop into a short REM sleep period, back to NREM sleep, then returning to REM sleep once again
Your brain goes through this cycle every 90 minutes
What changes is the ratio of NREM to REM sleep as you move through the night, with your sleep cycle comprised of more REM sleep during the second half of the night
If you wake up two hours earlier than usual, you aren’t just losing 2 hours of sleep - you could be losing 50, 60, or even 70% of your REM sleep
All stages of sleep are critical and perform different functions for the brain and body at different times of night
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