American neuroscientists have found that a person's memory of things they have lived or learned during the day can be noticeably improved by stimulating the so-called sigma rhythms during sleep using alternating current, according to an article published in the journal Current Biology.
“We have developed a special non-invasive brain stimulation system - a set of electrodes that are attached to the head. It produces a set of extremely weak electrical impulses during sleep, at the moment when our memory is consolidated.
As it turned out, the stimulation of electrical surges during this time, the so-called sigma rhythm, improved the memory of the volunteers, said Flavio Frolich of the University of North Carolina at Chapel Hill (USA).
Full sleep, combining the phases of REM sleep, when a person or an animal "replays" in memory the events of the past day, and slow sleep, when our body is completely numb, has been considered until now a distinctive feature of mammals and birds. The presence of sleep phases and the ability to “play” memories, as scientists believed, was a sign of a higher intelligence in birds and warm-blooded animals than in reptiles and amphibians.
As Frolikh notes, both phases of sleep have been well studied by scientists, however, neurophysiologists have not yet understood how memory is consolidated during REM sleep, and how we can contribute to this, or vice versa, make a person forget what he lived during the day.
One of the distinguishing features of REM sleep is the so-called sigma rhythms - spindle-shaped groups of bursts of brain waves with a frequency of 10 to 16 hertz, the strength of which gradually increases and then decreases. Scientists suspected that these structures on the EEG could be associated with the process of memory consolidation, but it was not clear whether these electrical vibrations contribute to the memorization of the past day, or are simply an "echo" of the synchronous activity of brain cells.
Frolikh and his colleagues tested which of these theories is correct using the system they created for "wireless" brain stimulation, which works not on direct, but on alternating current. This brain wave stimulator, the neurophysiologist explains, has one big advantage over conventional devices of this kind - it allows you to amplify or suppress brain waves of only one type, without affecting the work of others.
Using a similar emitter, the scientists tested what would happen to the memory of several volunteers if their sigma rhythms were increased during sleep. Before going to bed, as Frolikh says, his wards had to pass two memory tests - remember the associations between pairs of words and reproduce the "fraction" knocked out by the experimenter's fingers.
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As the experiment showed, the stimulation of sigma waves improved the memory of the volunteers - for example, they began to recall the sequence of finger strikes much more often and correctly. Interestingly, their associative memory did not improve, and they memorized words as poorly as before the start of stimulation or after a false stimulation, which was not actually done.
According to Frolikh, achieving such a result suggests that brain waves do affect the process of memory consolidation and suggest that we can control this process by stimulating the brain. In the near future, his team will try to use the device they have created to stimulate memory in people suffering from schizophrenia or Alzheimer's disease, which could help restore them to full life.
