Stages of Sleep

Your brain is actually quite busy while you are sleeping. States of your brain activity during sleep and wakefulness result from different activating and inhibiting forces that are generated within your brain.

Sleep is a dynamic process characterized by distinct states defined by different set of brain waves. There is a dream state characterized by movement of the eyeballs even if the eyes are closed.  This is called REM or Rapid Eye Movement. The other stages are collectively called Non-REM or NREM stage and they from Stages 1 to 3 with Stage 3 being the “deepest” sleep.

NREM SLEEP

• Stage 1 is about 5% to 10% of your sleep time and this is the transition between wakefulness and sleep. At this stage, you will be easily awakened.
• Stage 2 is about 40% to 50% of your sleep time. At this stage, your brain waves slow down with occasional bursts of rapid waves.
• Stage 3 is about 20% of your sleep time. At this stage, extremely slow brain waves appear and you are in deep sleep where all eye and muscle movement stop.

REM SLEEP

Follows NREM sleep, this stage is about 20% – 25% of your sleep time and occurs 4-5 times during your normal 8- to 9-hour sleep period.

Your first REM period of the night may be less than 10 minutes in duration, while the last may exceed 60 minutes. REM is usually associated with dreaming. Your eyeballs move rapidly, your heart rate and breathing become rapid and irregular, and your blood pressure rises. The muscles of your body are virtually paralyzed and your brain is highly active.

The graph below shows the electrical activity recorded in your brain during REM sleep and this is also similar to that which is recorded during wakefulness.

Source: Henry G. Raroque, MD. (2014). Lecture notes on Introduction to Sleep. The Dallas School of Neuroscience and Sleep Medicine, Texas.