January 15, 2025

Andrew Georgy 

9th Grade

Fountain Valley High School

Basics of Sleep

It’s been a long day. Having been finally rewarded by the peacefulness of nighttime, you pull up the covers and snuggle up with your favorite stuffed animal, ready to power off and sleep into the night. Yet as you doze off, your brain hits the restart button, rewiring and untangling all the information and inputs it has received all day.

Sleep is an essential process we all (hopefully) partake in daily. However, contrary to popular belief, it’s the most active time for most of our brains, especially memorization hubs and emotional centers. Specifically, the hippocampus (which is critical in forming memories), the parahippocampal cortex (which aids the hippocampus), the amygdala (where emotional information is registered), and the anterior cingulate (which helps regulate emotions) are the four regions of the brain that are most active during the sleep cycle. 

However, your brain isn’t emitting the same waves during all five cycles of sleep; rather, it focuses on different waves during non-REM (rapid eye movement) and REM sleep. Non-REM sleep is defined as the beginning stages of sleep; your eyes don’t twitch, and your brain is still “calming down” before it enters REM sleep. REM sleep is a deep sleep since your eyes twitch and you dream of vivid pictures. 

An Intro into Cycles and Your Circidian Rythym

Five stages of sleep repeat when you sleep, usually for 5-6 cycles that last 90-110 minutes per cycle. The five stages are divided between REM and non-REM sleep; three stages are non-REM, while the last two are. The five stages contain many differences, including different brain waves and K-complexes' appearance (more on that in Stage 2). They are driven by the circadian rhythm (the body’s natural sleep-wake cycle over 24 hours), which is derived from the suprachiasmatic nucleus or SCN. The SCN (a clump of cells in the hypothalamus just above the optical chiasm) uses light inputs from your eyes to send messages to the rest of the body on when to sleep or wake up. But what are the different characteristics of each form of sleep, and how does our brain function during each stage?

Stage One

Stage 1 is characterized by three things: slower heart rate, lower body temperature, and decreased muscle tension. It is more of a transitional phase between wakefulness and sleep, meaning it’s when we start getting sleepy and turn off the lights. 

Brain activity in stage one starkly contrasts with that when you are awake, as both alpha and theta waves are emitted instead of the normal beta waves produced when you are awake. The early portion of stage one forms low-frequency synchronized high-amplitude alpha waves. 

As you progress further into stage one sleep, theta waves (which have a lower frequency than alpha waves) increase in output as you try to emerge into the second stage; however, if you are waked in this stage, you might not even realize you are sleeping as you have not yet entered stage two.

Stage Two

In stage two, the body enters a stage of deep relaxation. Theta waves are still emitted, but they are “interrupted” by sleep spindles, or brief explosions of activity. These spindles are characterized by a rapid burst of higher-frequency brain waves (which scientists and researchers believe could be key to learning and memorization). 

As stated before, K-complexes also often occur in stage two. K-complexes are extremely high-amplitude patterns of brain activity that are usually a response to environmental stimuli, such as noise or light. 

Stage Three

Stage three encompasses the first stage of deep sleep and is known for low high amplitude and decreased frequency (usually less than three Hz) delta waves. Just like in stage one, heart rate and respiration levels slow dramatically; however, it’s much harder to wake someone up in this stage compared to the earlier stages. In fact, numerous people who contain high levels of alpha waves do not feel satisfied or refreshed from any sleep if they are awakened in stage three. 

Stages Four and Five

It’s hard to draw a difference between REM sleep and non-REM sleep when it comes to brain activity; as a matter of fact, stage four was considered to be a part of non-REM sleep until 2008. However, these stages are characterized by dreams and eye movement compared to the other stages. In these stages, three unusual actions happen: alpha waves are emitted despite the person not being awake, unnecessary muscles for survival or respiration are paralyzed, and it tends to increase as the night goes on. It’s also common for a person deprived of REM sleep to “catch up” when they have an opportunity, showing that our bodies tend to lean towards REM sleep more. Although there isn’t a clear reason why (even researchers debate its significance), some scientists have suggested that it may be because more vital processes such as memorization are more prevalent in REM sleep.