Sleep precedes the evolution of the brain.Hydra is living evidence

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Hydra is A simple creature. Less than half an inch long, its tubular body has a foot on one end and a mouth on the other end. The feet are close to the surface of the water — possibly plants or rocks — and the mouth is full of tentacles, trapping passing daphnia. It doesn’t have a brain, or even a lot of nervous system.

but, New research shows, It slept. Research conducted by a team in South Korea and Japan has shown that Hydra periodically enters a state of rest that meets basic sleep standards.

On the surface, this seems unlikely. For more than a century, researchers studying sleep have been searching for its use and structure in the brain.They explored the relationship between sleep and Memory and learningThey numbered the neural circuits that pushed us into unconscious sleepiness and pulled us back from it. They recorded the obvious changes in brain waves that marked our different stages of sleep and tried to understand what drives them.A lot of research and people’s daily experience have proved that human sleep Connection with the brain.

However, the opposite of this brain-centered view of sleep has emerged.The researchers noticed that by muscle with Some other organizations The external nervous system can regulate sleep. Sleep generally affects the metabolism in the body, which shows that its effects are not only on the nervous system. Research that has been quietly developing for decades has shown that simple organisms with fewer and fewer brains spend a lot of time doing things that look a lot like sleep. Sometimes, their behavior is simply classified as “like sleep,” but as more details are discovered, it becomes increasingly unclear why this distinction is necessary.

Simple-looking creatures—including the brainless Hydra today—can sleep. The interesting implication of this discovery is that the original function of sleep, buried in the history of life billions of years ago, may be quite different from the standard human conception of it. If sleep does not require the brain, then it may be a broader phenomenon than we thought.

Understanding sleep

Sleep is different from hibernation, coma, drunkenness, or any other state of stillness, French sleep scientist Henri Piéron wrote in 1913. Our conscious experience is particularly mysterious. Without it, people will be confused, confused, and unable to think clearly. For researchers who want to learn more about sleep, understanding the role of sleep on the brain seems essential.

Therefore, in the middle of the 20th century, if you want to study sleep, you will become an expert reader of EEG or EEG. By placing electrodes on humans, cats or mice, researchers can clearly and accurately determine whether subjects are sleeping and which stage of sleep they are in. This method has generated many insights, but it has left a bias in science: almost all the knowledge we know about sleep comes from animals that can be fitted with electrodes, and the characteristics of sleep are increasingly based on the brain activity associated with them To define.

This frustration Irene ToblerIn the late 1970s, a sleep physiologist working at the University of Zurich, he began to study the behavior of cockroaches, wondering whether insects and other invertebrates sleep like mammals. After reading Piéron and others’ books, Tobler knew that sleep can also be defined by behavior.

She refined a set of behavioral standards to identify sleep without EEG. Sleeping animals will not move around. It is more difficult to wake a person than to simply rest. It may adopt a different posture than when it is awake, or it may look for a specific sleeping position. Once awakened, it will behave normally instead of sluggish. Tobler derived his own standard from her research on mice: Sleeping animals will sleep longer or deeper than usual after being disturbed. This phenomenon is called sleep homeostasis.

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