James' World 2

Rapid eye movement, or REM sleep, is the final phase of the four stage cycle that occurs during sleep. Unlike non-REM sleep, the fourth phase is characterized by an increase in brain activity and autonomic nervous system functions, which are closer to what is seen during the awakened state. Similar to non-REM sleep stages, this stage of sleep is primarily controlled by the brainstem and hypothalamus, with added contributions from the hippocampus and amygdala. Additionally, REM sleep is associated with an increase in occurrence of vivid dreams. While non-REM sleep has been associated with rest and recovery, the purpose and benefits of REM sleep are still unknown. However, many theories hypothesize that REM sleep is useful for learning and memory formation.

Key Takeaways: What Is REM Sleep?

• REM sleep is an active stage of sleep characterized by increased brain wave activity, return to awake state autonomic functions, and dreams with associated paralysis.
• The brainstem, particularly the pons and midbrain, and the hypothalamus are key areas of the brain that control REM sleep with hormone secreting “REM-on” and “REM-off” cells.
• The most vivid, elaborate, and emotional dreams occur during REM sleep.
• The benefits of REM sleep are uncertain, but may be related to learning and storage of memory.

 

REM Definition

REM sleep is often described as a “paradoxical” sleep state due to its increased activity after non-REM sleep. The three prior stages of sleep, known as non-REM or N1, N2, and N3, occur initially during the sleep cycle to progressively slow bodily functions and brain activity. However, after the occurrence of N3 sleep (the deepest stage of sleep), the brain signals for the onset of a more aroused state. As the name implies, the eyes move rapidly sideways during REM sleep. Autonomic functions such as heart rate, respiratory rate, and blood pressure begin to increase closer to their values while awake. However, because this period is often associated with dreams, major limb muscle activities are temporarily paralyzed. Twitching can still be observed in smaller muscle groups.

REM sleep is the longest period of the sleep cycle and lasts for 70 to 120 minutes. As the duration of sleep progresses, the sleep cycle favors increased time spent in REM sleep. The proportion time spent in this phase is determined by a person’s age. All stages of sleep are present in newborns; however, babies have a much higher percentage of non-REM slow wave sleep. The ratio of REM sleep gradually increases with age until it reaches 20-25% of the sleep cycle in adults.

 

REM and Your Brain

During REM sleep, brain wave activity measured on an electroencephalogram (EEG) also increases, as compared to the slower wave activity seen during non-REM sleep. N1 sleep shows slowing of the normal alpha wave pattern noted during the awake state. N2 sleep introduces K waves, or long, high voltage waves lasting up to 1 second, and sleep spindles, or periods of low voltage and high frequency spikes. N3 sleep is characterized by delta waves, or high voltage, slow, and irregular activity. However, EEGs obtained during REM sleep show sleep patterns with low voltage and fast waves, some alpha waves, and muscle twitch spikes associated with transmitted rapid eye movement. These readings are also more variable than those observed during non-REM sleep, with random spiking patterns at times fluctuating more than activity seen while awake.

The major portions of the brain activated during REM sleep are the brainstem and the hypothalamus. The pons and midbrain, in particular, and the hypothalamus contain specialized cells known as “REM-on” and “REM-off” cells. To induce the transition to REM sleep, REM-on cells secrete hormones such as GABA, acetylcholine, and glutamate to instruct the onset of rapid eye movements, muscle activity suppression, and autonomic changes. REM-off cells, as their name implies, induce the offset of REM sleep by secretion of stimulatory hormones such as norepinephrine, epinephrine, and histamine.