REM vs NREM | Non REM Sleep vs REM Sleep | Paradoxical sleep (or Desynchronized sleep) vs Slow Wave Sleep
Sleep is a state of unawareness from which the person can be aroused by sensory or other stimuli. Sleep is essential for the life since it is the time when the body rests and restores its energy levels. For the good health, a person should have sleep of 6-10 hours, but there are variations in individuals.
During a sleep wake cycle, the person goes through a series of different stages of sleep. The two main types are REM (Rapid eye movement) and non-REM/slow wave sleep. The latter is further divided in to four stages namely stage I, II, III and IV. This article points out the differences between REM and non-REM sleep during a sleep-wake cycle.
REM sleep also known as paradoxical sleep or desynchronized sleep comprises about 20% of an adult sleep. The percentage is highest during infancy and early childhood (50%) and declines as the person ages. Normal sleep-wake cycle consists of 4-5 episodes of REM sleep in which the interval between REM episodes reduces but the duration increases as the cycle progress.
Usually REM sleep starts 90min after the onset of sleep. The first period lasts for about 10min with each recurring REM stage lengthening, and the final one may last up to an hour. During this sleep, due to heightened brain activity intense dreaming occurs. Simultaneously paralysis of the major voluntary muscle groups is seen. Increased body movements, particularly rapid eye movements, occur during this sleep. Heart rate and respiration may become irregular. Tachycardia, hypertension, penile erection, teeth grinding are seen.
EEG changes are similar to alert/awake state and beta waves appear.
Non REM Sleep/Slow Wave Sleep
This sleep comprises four stages each lasting 5-15min and in a completed sleep wake cycle progression from stage 1-4 is seen before REM sleep is attained. Depth of non REM sleep decreases as the cycle progress.
It is a restful sleep where the body repairs and regenerates tissues, builds bone and muscle and appears to strengthen the immune system. Reduction of body movements, vascular tone, respiratory rate, metabolic rate and blood pressure by 10-20% occur during this phase. Sleep walking (somnambulism), bed wetting (nocturnal enuresis) and nightmares are seen too. Subjects may see dreams, but when awake they cannot remember them.
Specific EEG changes occur. No beta waves. Theta and delta waves are present.
What is the difference between REM and NREM?
• REM is similar to an alert state, but NREM is a restful sleep.
• REM usually comprises 20% of adult sleep, but most of the time sleep is of NREM.
• During REM sleep brain is excited but muscles tone is reduced where it is given the name paradoxical sleep.
• Dreams are seen in REM sleep but in NREM subject may see dreams without remembering them.
• Increased sympathetic activities are seen during REM sleep.
• Sleep walking, bed wetting and nightmares are seen in NREM sleep.
• Theta and delta waves are seen in NREM sleep, but beta waves appear in REM sleep.