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REM: When the Brain is Awake in Sleep

REM (Rapid Eye Movement) sleep is one of the sleep cycle's most intriguing and essential phases. It alternates with the non-REM (NREM) sleep stages throughout the night, forming cycles of approximately 90 minutes. During each cycle, we go through stages that vary in depth and characteristics, and REM sleep stands out as a paradoxical phase. In this phase, the brain presents electrical activity similar to wakefulness despite the body being in a deep state of rest.


In REM sleep, one of the most striking characteristics is the presence of rapid eye movements. These movements are accompanied by muscular hypotonia, which means that the muscles, especially the skeletal ones, are almost entirely paralyzed. This atony is crucial to prevent the body from physically acting out dreams, which are more common and intense during this phase. Although the body is practically immobile, the brain is highly active, which can result in vivid dreams with emotional and sensory content. Furthermore, during REM sleep, breathing and heart rate become more irregular, and there is an increase in cerebral blood flow, indicating that the brain is not just resting but processing information and performing essential functions.


Dreams, in turn, are an intriguing manifestation of brain activity during REM sleep. They can involve various sensory experiences, such as visual images, sounds, emotions, and even tactile sensations. Although the exact meaning of dreams has not yet been definitively explained, they are believed to play a fundamental role in memory, learning, and the reorganization of brain circuits, helping to consolidate information acquired during the day and facilitating brain plasticity. In addition, dreams have a physiological impact, such as activating the autonomic nervous system, related to intense emotions such as fear or excitement.


The sleep cycle is a process of rest and involves cellular repair and restoration of cognitive and emotional functions. REM sleep, in particular, has been associated with emotional processing and maintaining mental health, as it is during this stage that the brain appears to reorganize memories, reflect on experiences, and even integrate emotions.


However, the amount of REM sleep a person experiences throughout the night can vary, and this sleep cycle tends to be more concentrated in the last few hours of rest. Initially, REM sleep lasts only a few minutes and then increases throughout the night. REM sleep accounts for about 20-25% of total sleep in adults but can account for a more significant proportion in newborns. As we age, the architecture of sleep changes, with a reduction in deep sleep and an increase in nocturnal awakenings.


Under normal conditions, the sleep-wake cycle is regulated by circadian rhythms and influenced by light, melatonin secretion, and body temperature, all of which help the body adjust to its natural day-night cycle. Disruptions, such as those caused by night work or time zone changes, can alter these cycles and affect sleep quality, impairing the amount of REM sleep and resulting in daytime sleepiness, irritability, and cognitive difficulties.


REM sleep is, therefore, a crucial phase not only for physical rest but also for maintaining mental and emotional functions. It reminds us of the complexity and importance of sleep, which goes far beyond a simple biological need and plays a fundamental role in our health and well-being.



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