People have one common misconception about sleep, and hardly believe that there are stages of sleep. It is believed that sleep is just when the body “turns off” for some hours, and then “turns back on”. Sleep is looked at as a reflexive and constant process. That is certainly not the case. Sleep is a genuinely active state. Apart from the body constantly moving while asleep, the brain activity is much more varied than the normal “awake” state.
The Tool to Measure Stages of Sleep
The electroencephalograph is a tool researchers use in order to measure the stages of sleep. Its invention made it possible for scientists to study sleep in ways that were not possible before. A graduate named Eugene Aserinsky used the electroencephalograph to discover the REM sleep in the 1950’s. Further researches on sleep have shown that sleep has a series of stages it progresses through, which display different wave patterns. There are two types of sleep mainly:
- Rapid Eye movement (REM) sleep (paradoxical or active sleep)
- Non- Rapid Eye movement (NREM) sleep (quiet sleep)
Every sleep cycle lasts for about 90 to 120 minutes, and comprises of 4 stages. In some studies, the first 5 to 10 minutes are also considered as a stage, but it is more of a transitional stage when people are beginning to fall asleep. This transitional stage does not repeat itself, unlike the other four stages, which keep repeating throughout the night.
Dreams occur in any of the 4 stages, but the most memorable and vivid ones are in the last stage (i.e. REM sleep). The cycle can repeat about 4 to 5 times on an average per night, and possibly 7 times at most. This explains how people end up having different dreams in one night. However, people usually tend to remember dreams they have closer to their waking time.
People are normally awake and alert during the earliest phase of sleep. The brain produces some fast and small waves (beta waves), which begin to turn into slower waves (alpha waves) and relax the brain. During this period, people are not exactly asleep and experience some vivid and strange sensations called “hypnagogic hallucinations”. Examples of these hallucinations are when people feel like they can hear someone calling them or like they are falling. Another common thing seen during this period is a startling jerk (myoclonic jerk).
The Stages of Sleep:
This is a light stage of sleep, which occurs at the beginning of a sleep cycle. It is a transition period between the wakefulness and sleep process. In this stage, the brain produces very slow waves called theta waves, which have high amplitude. During this period, the person’s sleep lasts only for a brief moment, like for around 5 to 10 minutes. When people are awakened in stage 1, they may claim that they weren’t asleep, because they would have been alert and well aware of what’s going on in their surroundings.
In stage 2, a person’s sleep lasts for only 20 minutes approximately. At this stage, the brain produces rapid bursts of brain waves which are rhythmic. This wave activity is called “sleep spindles.” During the stage 2, the heart rate begins to slow down and the body temperature decreases.
The brain begins to produce the “delta waves” in stage 3. These are deep and slow brain waves that send the person into a transition state of deep sleep, but a very light sleep at the same time.
This stage of sleep is also known as “delta sleep” sometimes. That is because of the “delta waves” produced by the brain during this stage. During this time, an individual’s sleep lasts for 30 minutes approximately. It is towards the end of this period that disorders like bedwetting and sleepwalking occur.
It is during this 5th stage of sleep when most of the dreaming takes place. This is called the REM (rapid eye movement) sleep. It is characterized by increased brain activity, increased rate of respiration and rapid eye movement. Dreaming also occurs during this stage due to the increase in brain activity; however, voluntary muscles tend to get paralyzed.
Sequence of the Stages
The entire sleep process starts from stage 1, then progresses into the 2, 3 and 4th stages. After the 4th stage, the process reverses back to stage 3 and 4, before getting into REM sleep. After the REM sleep, the body often returns back to stage 2 again. This sleep cycle keeps on repeating these stages around 4 or 5 times approximately, throughout the night.
However, it is important to realize that these stages of sleep cannot be said to have a precise sequence, due to their rampant and repetitive nature.