Have you ever wondered what’s going while you’re sleeping? Well the truth is there is a lot going on during the period of time you are asleep and it is divided into five stages. Using an electroencephalograph (EEG) we can determine the stage of sleep we are in.
A sleeping baby by oksidor via Flickr Creative Commons
Early stages of sleep prior to stage one:
Before phase one, our mind is relatively alert and therefore we experience hypnagogic hallucinations, such as experiencing the sensation of falling, and myoclonic jerks, an involuntary twitching of the muscles. Furthermore, our brain starts to produce small and fast waves known as beta waves. As the mind slowly beings to relax, slower waves called alpha waves are produced.
Stage one:
During this period, we are in the relatively light stage of sleep, and is often considered as the transition between being awake and falling asleep. It lasts for a brief amount of time, and usually when people wake up during this stage, they feel like they haven’t slept at all. The waves that are produced during this time is called theta waves, which are slow, high amplitude waves.
Stage two:
The body temperature starts to drop and heart rate slows down. At the same time the brain produces short periods of quick rhythmic waves known as sleep spindles.
Stage three:
This is the period between light sleep and deep sleep. Slow, deep waves called delta waves are produced.
Stage four:
Delta waves continue to be produced, therefore this period is also known as delta sleep. This stage typically lasts for about half an hour and we fall into a deep sleep. Generally bed-wetting and sleepwalking occurs during this stage.
Stage five:
This phase is commonly known as rap eye moment (REM) and we enter this stage approximately 90 minutes after falling asleep. Typically we enter REM sleep four to five times during the night, and each time the duration of REM sleep increases. During this period, the muscles become relaxed to a point where the body is paralyzed while respiration rate and brain activity increases. Due to the increase in brain activity, this is the time when most of our dreams occur.
Here is an example of what an EEG looks like:
EEG when awake and during the different stages of sleep via http://www.nature.com/nri/journal/v4/n6/fig_tab/nri1369_F1.html
Although the above EEG depicts the stages of sleep from stage one to five in order, the stages do not actually occur in this sequence. After falling asleep, we begin in stage one, and progress into stages two, three and four. After stage four, stages three then two is repeated prior to entering REM sleep. After REM sleep, we return to stage two. Throughout the night we cycle through the above sequence four to five times.
Below is a video about the five stages of sleep:
From YouTube user: Shannon Leigh
Now that you know more about the different stages of sleep, the next time you watch The Big Bang Theory and Sheldon mentions REM sleep, you’ll know what he’s talking about!
– Alice Lin
