People spend around a third of their lives sleeping. Persistent lack of sleep not only spoils the mood, but can also have serious consequences for your health.
However, it has hardly been clarified why we actually do regular sleep need. American researchers have now got to the bottom of this. Her conclusion in the journal “Science Advances”: While sleep is important for learning processes in the brain in early childhood, the focus is later on its repair.
Mice sleep five times longer than elephants, Babys need more sleep than adults and in dolphins and migratory birds only one half of the brain sleeps while the other is awake. All of those phenomena belong to the mysteries which, in some cases, still pose a mystery to science.
We cannot live without sleep
It is clear that sleep is essential for survival: this was confirmed by the experiment by sleep researcher Allan Rechtschaffen, who showed in the 1980s that rats that were permanently prevented from resting died after a few weeks.
In humans, short-term sleep deprivation leads to decreased reaction speed and concentration problems, while chronic ones Trouble sleeping With depressions, Overweight, Cardiovascular diseases and one weakened immune system be associated.
The more important is the question of what functions sleep actually fulfills. Scientists from the universities of Texas and California and the Santa Fe Institute headed by mathematician Junyu Cao have now carried out a statistical analysis with the data from more than 60 sleep studies, which included both humans and mammals. They evaluated data on the total duration of sleep, times in different sleep phases as well as brain– and height.
The task of sleep changes
The team, consisting of neurologists, biologists and statisticians, developed a model that explains why sleep time across different species decreases the larger the brain gets. Specifically, the researchers identified a point that occurs in humans at the age of 2.4 years and from which the function of the night’s rest fundamentally changes: from reorganization to repair. This fits in with the results of previous studies showing several important transitions in brain development in children between the ages of two and three.
Up to this age the brain grows rapidly. During REM sleep, which is characterized by rapid eye movements and dreams, the brain is busy making and strengthening synapses. These are the structures that connect the nerve cells with each other and allow them to communicate. “Babies should not be awakened during REM sleep because important work happens in their brains while they are sleeping,” commented biologist and co-author Gina Poe in a communication published on the study.
After about 2.4 years, however, the main purpose of sleep changes – and rapidly. Instead of building synapses, from now on and for the rest of life it is mainly about maintaining and repairing the brain. In fact, a certain neurological damage to the brain during waking hours is normal in humans and animals. Theoretical physicist and co-author Geoffrey West explains that sleep helps to repair this damage – like subway trains that are maintained and repaired at night so as not to obstruct traffic during the day.
Those maintenance activities mostly happened during non-REM sleep. Correspondingly, its share increases from the age of 2.4 years in humans, while the duration of sleep decreases overall. Newborns, for example, spend around 50 percent of their sleep in the REM phase, while this proportion falls to 25 percent at the age of ten and finally 15 percent for people over 50 years of age.
“Sleep is as important as food,” summarizes biologist Poe. “And it’s amazing how well sleep meets the needs of our nervous system. Everyone from jellyfish to birds to whales sleeps. While we sleep, our brains don’t rest.”
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