REM sleep is a phase of the five-stage sleep cycle, during which rapid eye movement (REM) occurs. Typically, there are three to five REM cycles during a night's sleep, the first lasting about ten minutes and the last, before waking, up to an hour. The deepest stage of REM sleep is where dreams occur. It is necessary to cycle through REM sleep to feel rested, and experts report adults 18 and older require 1.5 to 1.8 hours of this deep sleep per night.
During REM sleep, the brain exercises neural connections crucial to overall well-being and mental and physical health. REM sleep is also considered the learning phase of the cycle, as this is when the brain integrates and processes information from the day and prepares to store it in long-term memory. Lack of REM sleep can adversely effect the brain and cognitive function.
Most dreaming occurs during REM sleep, with about two hours spent dreaming each night. Signals from an area at the base of the brain, known as the pons, kickstart REM sleep. The signals then travel to the thalamus, which relays them to the cerebral cortex. The cortex is the layer of the brain responsible for organizing information while awake. Some scientists believe dreams are fragmented brain activity caused by the cortex's attempt to interpret the signals it receives from the pons during REM sleep.
During REM sleep the body is paralyzed, preventing the dreamer from acting out dreams and preventing injury. As detailed in a study by the University of Toronto, two brain system chemicals work together to paralyze the skeletal muscles during REM sleep. The neurotransmitters glycine and GABA work by shutting off motor neurons.
During REM sleep, the eyes move as if they are looking at something. Interestingly, even people who are blind move their eyes during REM sleep. They do not have "visual" dreams, but the brain activates in a way that imitates visual stimulation. There are studies that try to determine if this eye movement is really due to "scanning" images in dreams, or if it has another physiological reason. Regardless, researchers note that eye movements during REM sleep resemble the eye activity seen when people are shown or asked to remember images when awake.
While some people find a nightcap helps them fall asleep, both alcohol and drugs can interfere with neurotransmitters involved in sleep. Research on the effects of drinking and sleep published in Alcoholism: Clinical and Experimental Research, shows that while one drink will shorten the time it takes to fall asleep, that is offset by more disrupted deep sleep in the second half of the night.
A University of California study on napping proposes that REM sleep helps the brain create connections between unrelated ideas, improving creative problem-solving. The researchers theorize that a reduction in the amount of the neurotransmitters norepinephrine and acetylcholine during REM sleep may help integrate information into associative pathways in the brain. Conversely, when awake, the levels of these two neurotransmitters are higher, contributing to inhibited connections in the neocortex.
A study published by the National Institute of Neurological Disorders and Stroke reports that preventing rats from getting enough REM sleep significantly shortens their lifespan, from two or three years to five weeks. In humans, lack of REM sleep can lead to fatigue, weight loss or gain, and clumsiness during the day, and have a deleterious effect on the brain and cognitive functioning.
During other phases of sleep, blood pressure and heart rate decrease, but during REM sleep both increase. Experts hypothesize that this is a response to dreaming. REM sleep is sometimes called the "paradoxical sleep," because the body arouses some systems but temporarily paralyzes the muscular skeleton and limbs.
REM Behavior Disorder (RBD) leads to a failure of the mechanism that paralyzes the muscular-skeletal system for most people during REM sleep. This is possibly due to a malfunction in the brain stem. Those with RBD act out during REM sleep, sometimes punching, kicking, yelling and even leaping, resulting in injury to the person doing it, or their bed partner. People with RBD often have disorders like narcolepsy and sleep apnea, as well.
The rebound effect is a lengthening of REM sleep after periods of sleep deprivation. It is so important to brain function that the body has a built-in mechanism to make up for lost time. Extended REM sleep phases can result in more vivid dreams, nightmares, and a groggy, disconnected feeling in the morning.
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