Scientists of the Weizmann Institute of Science discovered: a certain type of learning is possible while sleeping

Prof. Noam Sobel and research student Anat Arazi from the Weizmann Institute of Science, proved that the connection between smells and sounds is learned during sleep

Is it possible to study while sleeping? In a study published today in the scientific journal "Nature Neuroscience", Prof. Noam Sobel and research student Anat Arazi from the Weizmann Institute of Science show that the connection between smells and sounds is learned during sleep. It turns out that when certain smells are presented after sounds during sleep, people begin to smell when they hear only the sounds - even in the absence of the smell. This phenomenon occurs both during sleep and wakefulness. In other words, people are able to learn new information while they sleep, which may unconsciously influence their behavior when they are awake.

In the story "The Profession" by Isaac Asimov, from 1957, a society is described where all learning is done by technological means, while sleeping. The need to "collect information" independently and individually shocks everyone who hears about this "primitive" option. According to this story, this is the face of reality in the 65th century. But in the meantime, in the 21st century, experiments in learning while sleeping are particularly complex. For example, the researcher must make sure that the volunteers are really asleep, and stay that way during all the "lessons".

The most rigorous experiments of verbal learning during sleep, failed to show a process of absorption of new information. Although more and more studies show the importance of sleep in learning and forming memories, no one has been able to prove that there is learning of new information in the adult brain while sleeping.

The members of Prof. Noam Sobel's research group in the Department of Neurobiology, in collaboration with doctors and researchers from Levinstein Hospital and the Tel Aviv-Jaffa Academic College, decided to conduct an associative learning experiment (conditioning) that involves exposing people to a sound and immediately afterwards to a smell, so that they "learn" connect the two - and respond to both at the same time. The use of sounds and escapes had several advantages. They do not wake up the sleeping person (in fact, there are smells that even promote good sleep), but the brain processes them and even reacts to them while sleeping. In addition, the sense of smell offers a non-verbal measure that can be observed - sniffing. The researchers found that in the case of the sense of smell, the sleeping brain behaves as in waking hours: we inhale deeply in the presence of a pleasant smell, but hold our breath when we smell a bad smell. This variation in sniffing could be recorded both while sleeping and awake. This type of learning, even though it seems simple, is related to brain areas responsible for certain higher functions - including the hippocampus, an area involved in creating memories.

In their experiment, the volunteers slept in a special laboratory while their sleep status was monitored. Waking up during conditioning - even for a moment - invalidated the results. During this sleep, the participants heard a certain sound, followed by a smell - sometimes pleasant and sometimes unpleasant. After that, another sound was heard, followed by the smell again. This time, the smell has the opposite degree of pleasantness. During the night, this conditioning was partially reinforced, so that sometimes the volunteers were exposed to sounds only - no smell. The sleeping volunteers responded to these sounds as if accompanied by a bolt - with deep or shallow inhalations.

The next day, after waking up, the volunteers heard the sounds again - without the accompanying smells. According to their reports, they did not remember the sounds and smells - but their sniffing patterns told a completely different story: when hearing the sounds that were associated with pleasant smells, they inhaled deeply, while the other sounds - those that came before the bad smells - caused short, shallow inhalations.

The researchers then asked whether this type of learning was associated with a particular stage of sleep. In a second experiment, they divided the sleep cycles according to rapid eye movement (REM) sleep and non-REM sleep, and then activated the conditioning in one phase only. To their surprise, they found that the conditioned response was stronger during the TAM phase, but the transfer of the association from sleep to wakefulness occurred only in sleep without TAM. The scientists believe that during the sleepless night, we may be more affected by the stimuli in our environment, but "dream forgetfulness" - which causes us to forget most of our dreams - may affect any learning that occurs during this stage of sleep. On the other hand, sleep without TAM is an important phase for forming memories, and it is possible that it also plays an important role in this type of learning while sleeping.

This study, which was carried out in Prof. Noam Sobel's laboratory, focused on the sense of smell. But in her future research, Anat Erzi plans to expand the scope and investigate the processes of processing sensory information in the brain in different states of consciousness, including sleep and coma. In addition, they will try to find out what else can be absorbed while sleeping. Anat Arzi: "Now that we know that at least one type of learning is possible during sleep, we want to know where the limit is - what information can be learned in sleep and what cannot."