Our sleep may seem like “switching off” or being quite a steady state, when our mind and body remain dormant and our brain activity is ceased. However, in the middle of the twentieth century it was discovered that every healthy sleep has its special architecture. When we sleep, our mind goes through a sequence of 5 stages, which can be characterized by different brain wave patterns. In 1953, the invention of a device called the electroencephalograph helped the scientists discover two types of sleep:
1. REM (rapid eye movement) sleep, or dreaming stage, which can be characterized by increased brain activity and rapid movement of our eyes under the eyelids.
2. NREM (non-REM) sleep, when our brain activity slows down during sleep.
Adult people spend about 20% of their sleep in REM phase, and infants spend about 50% of their sleep in this phase. This is the stage when we see the brightest and the most vivid dreams that our brain creates from the pieces of information we know and everything we see during our life. NREM sleep lasts longer, and during this phase our body works for restoring our tissues and improving the work of all the body systems, recreating bones and muscles, etc. The stages of our sleep include the following 5 phases:
Stage 1. NREM or Slow Wave Sleep (SWS). It is a period of transition between wakefulness and sleep, so the sleep is very light and a person can be woken up easily. The eye movements slow down. On this stage some people experience sudden abrupt movements (so called hypnic myoclonia), and some people may have a sensation of falling down.
Stage 2. NREM or SWS. This is the longest stage which lasts for about 50% of the whole cycle. In this phase we are still in quite light sleep. At that, our body and mind get prepared for entering a deep sleep. Our eye movements stop, the body temperature decreases, and our heart rate and brain activity slows down.
Stage 3. NREM or SWS. This stage is called deep slow-wave sleep. On this stage, very slow brain waves (delta-waves) are generated. It is quite hard to wake up a person during this stage. There are no eye movements or muscle activities.
Stage 4. NREM or SWS. This is the second stage of deep sleep. The brain goes on producing very slow delta-waves. This stage usually lasts for about 30 minutes and possible sleepwalking or bedwetting occurs on this stage. Stages 3 and 4 are the most important stages of our sleep, and if they do not last long enough, the whole sleep will be not satisfying.
Stage 5. REM sleep. The REM period lasts for about 15 minutes and can be characterized with shallow and rapid breathing, increased heart rate and blood pressure, fast movements of the eyes and certain muscle activity. This is the stage when brain activity maximizes and the waves generated can be compared to the ones generated when a person is awake. That is why dreaming occurs, and, if awoken during the REM sleep, a person can remember the dreams very clearly.
Those are the stages of human sleep cycles, which every person, who does not suffer from sleep disorders, experiences every night. Since the whole cycle usually takes 80-90 minutes, during our night seep we go through 4-5 full cycles. The length of the stages aso changes during the course of the night sleep: for example, the REM stages of the later cycles tend to last a little longer, sometimes even up to 40-50 minutes. Therefore, the most vivid and exciting dreams usually come to our mind closer to the morning!