Bizarre experiments on sleeping volunteers helped neurophysiologists prove that a person can only remember new information during REM sleep, according to an article published in the journal Nature Communications.
“The question of whether a sleeping person can memorize new information has been exciting the minds of scientists for several decades. We were able to show that unconscious, latent memories can still form during sleep, but only during REM sleep and the transition period between REM and deep sleep. Similar stimulation in deep sleep, on the other hand, leads to opposite effects,”write Thomas Andrillon of the Pierre and Marie Curie University in Paris, France and his colleagues.
There are two types of sleep, REM and NREM sleep, which alternate with each other constantly. When falling asleep, the slow-wave sleep phase begins, during which the body gradually "turns off" and recovers.
During REM sleep, the body switches to "working mode", but all muscles are "turned off" for the sake of safety, and the person becomes absolutely immobile. This phase is characterized by rapid and chaotic eye movements and it is believed that it is at this time that people have the most vivid dreams.
For a long time, as Andrillon explains, scientists have been arguing about whether a person can memorize new information during REM sleep, or at this time all his senses are completely "turned off" and he cannot perceive information from the outside world. Many neurophysiologists believe that active perception of signals from the outside world will interfere with the consolidation of memory, and therefore the brain will either actively suppress them, making "internal" memories brighter, or simply ignore, removing information about external stimuli.
Andrillon and his colleagues checked whether this is really so in a highly unusual experiment in which several volunteers who agreed to spend one night in the laboratory of scientists had to find a special sequence of sounds "hidden" in white noise.
As a rule, any person can cope with this task, however, to successfully solve it, most of them need several dozen listening to such an audio recording. This feature of such a "noise test", as neurophysiologists called it, allowed them to test whether a person would be able to recognize this combination of sounds faster if played in a dream.
Guided by this idea, Andrillon and his colleagues divided the volunteers into several groups, connected them to electroencephalographs and placed them in special rooms, in which the speakers began to play a recording of "white noise" at the time when their brain entered one or another phase of sleep.
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As these experiments showed, volunteers listening to these noise "melodies" during REM sleep determined the sequence of sounds several times faster than they were able to do before the start of the experiments. On the other hand, playing these audio tapes during deep sleep only worsened the volunteers' memory and made them spend much more time searching for the sequence than before going to bed.
Similar results of experiments, as scientists note, indicate that a person is not completely "disconnected" from the outside world during sleep and continues to perceive and memorize information. Scientists believe that further observation of how the brain works during sleep can help us understand how memory works and how we can correct disorders in its functioning, including amnesia and the recently discovered Groundhog Day Syndrome.