When we wake up every morning, we do not always remember our dreams. Or we remember them partially. But what is the reason for such selective forgetfulness? According to researchers from the University of Nagoya (Japan), we forget our dreams with barely opening our eyes due to certain neurons that play a role in eliminating various diseases. Moreover, the activity of these neurons is observed during the phase of rapid sleep (REM), characterized by increased brain activity. One of the signs of which is the rapid movement of the eyeballs and vivid dreams.
About mice and people
In a study published in the journal Science, a research team from the University of Nagoya and colleagues from the National Institutes of Health detailed the processes that take place during REM sleep. It is known that the change in sleep phases depends on different neural and hormonal mechanisms, and therefore scientists knew what to look for. For example, in mice during REM sleep, more than half of the neurons synthesizing the sleep melanin-concentrating hormone MCH remained active in the hypothalamus, a region of the brain that controls sleep and hunger. But during wakefulness, only 35% remained active. This means that it is the MCH neurons that are important for REM sleep. According to scientists, this discovery is likely to be a breakthrough in determining why people tend to forget dreams.
It is believed that memories persist or disappear during sleep, but how exactly this happens has long been a mystery. Studying laboratory mice, the scientists found that activation of the end of axons - the processes of nerve cells that connect the neurons of the hypothalamus MCH to the hippocampus (the memory center of the brain), became the cause of inhibition of neurons in this area of the brain. The researchers then worked with mice whose genome had been genetically modified. This allowed specialists to “turn on and off” the activity of MCH neurons using chemicals. The team ran several tests, including using toys. Activation of MCH neurons during REM sleep impaired the memory of animals, and switching off neurons improved it.
During sleep, the brain decides which information to forget and which information to leave.
Further experiments showed that mice performed better on tests only when neurons were turned off during REM sleep. But when the animals were in the deep sleep phase, no effect was observed. There is a possibility that MCH neurons eliminate memories, causing inhibition of hippocampal neurons. Scientists believe the human brain works the same way. Moreover, it is possible that in the future the results obtained may lead to the development of a new method of treating post-traumatic stress disorder, by removing traumatic memories.
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A nice addition to this work was a recent study by scientists from the University of Freiburg. The team has discovered the neurons responsible for the fastest movement of the eyeballs during REM sleep. The study was also conducted on laboratory mice. It turned out that the discovered neurons are similar to the wings of a butterfly, which are associated with many nerve centers in the brain, as well as with the neurons of the MCH. The work was published in the journal Nature Communications.
Lyubov Sokovikova