Even in sleep, the brain understands and hears words

2024 Author: Seth Attwood | [email protected]. Last modified: 2023-12-16 15:55

I have a habit: sleeping under the TV. I turn on a channel and slowly fall asleep. It turns out to be harmful. You never know what the brain will remember from what it heard, not all information is equally useful. Be alert and think about the background that surrounds you in your sleep.

Experiments carried out by researchers at the Higher Normal School in Paris have shown that during a long period of slow wave sleep, we continue to unconsciously hear and understand words. The results of the work are described in an article published by The Journal of Neuroscience.

In a dream, we practically do not react to external stimuli and are unable to move: these processes are inhibited in the brain even at a "low" level. However, some stimuli can break through this blockage and cause us to wake up and return to consciousness. Perhaps the brain maintains a certain level of vigilance, monitoring the safety of the environment. This ability was studied by Sid Kouider and his colleagues.

For experiments, they selected 23 young healthy volunteers who slept in the laboratory under the supervision of scientists. To begin with, the experimenters read them various words (in their native language) and, using an electroencephalogram (EEG), monitored the brain activity of awake subjects while they pressed a button: under the left hand, if the word meant an object, and under the right, if the animal. This made it possible to establish patterns of electrical activity of the brain characteristic of each volunteer, associated with the movement of the left and right hands.

These experiments were then repeated during different sleep phases: light slow-wave sleep (the longest phase), deep sleep sleep, and REM sleep (during which we usually dream). EEG recording made it possible to find out whether the brain was reacting, trying to send a signal to the hand, whether it understood the spoken word. As it turned out, in REM sleep, the brain recognizes words only if they sounded at the first stage of the experiment; there was no response from the nervous system to the new words. With light slow sleep, the reaction was complete both to the words already sounded and to new words. On the other hand, no brain activity was noted during deep NREM sleep.

Scientists believe that the lack of response during deep NREM sleep is associated with a massive "shutdown" of brain neurons. At the same time, in REM sleep, the excitation of neurons by external stimuli competes with arousal caused by dreams. This weakens their reaction, and it occurs only in response to already familiar words, which more easily excite "trained" neural networks.

It is worth noting that the theory of "watch points" in the cerebral cortex that maintain wakefulness even in sleep conditions was put forward by the founder of the physiology of higher nervous activity, Nobel Prize winner Ivan Petrovich Pavlov. Experiments with hypnosis prompted him to such an idea: it is known that an ordinary dream can be turned into a hypnotic one and suggestions made in it, which, most often, are less remembered by the patient than under conditions of transfer of consciousness from wakefulness to an altered state, even without a special mindset for forgetting.