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Why do newborns spend more than half of their sleep in REM sleep?

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While the exact function of REM sleep remains a subject of scientific study, researchers hypothesize that the high proportion of time newborns spend in this stage—more than 50 percent of their total sleep—is essential for brain development.123

It has been suggested that the frequent occurrence of REM sleep in infants provides necessary internal stimulation to the central nervous system, facilitating its orderly maturation. This "active sleep," as it is often called in newborns, is characterized by brain activity that in some respects resembles wakefulness, potentially aiding in the plasticity and maintenance of the developing brain. As children mature, the percentage of time spent in REM sleep declines, reaching adult proportions of approximately 20 to 25 percent by around age two.13