Sleeping time is sometimes considered unproductive. This raises the question of whether sleeping time could be more productive, for example by learning a new language? To date, sleep research focused on the stabilization and strengthening (consolidation) of the memories that had been formed during the previous vigil. However, the learning during the dream rarely was examined. There is considerable evidence that the learned learning information is being recapitulated repeatedly in the sleeping brain. The repetition during sleep strengthens the traces of memory still fragile and embodies the newly acquired information in the pre-existing store of knowledge.
If sleep improves the storage of information that is heard, then the first reproduction, that is to say, the initial processing of new information, should also be feasible during sleep, and can carve a memory watch that lasted in a wake. This was the research question of Katharina Henke, Marc Züst and Simon Ruch from the Institute of Psychology and the Interphase Research Cooperation "Dream decoding" at the University of Bern, Switzerland. These researchers now showed for the first time that new foreign words and their translation words could be associated during a noon session with associations stored in a wake. After waking up, the participants could reactivate the associations formed by the dream to accede to the meanings of the word when they are represented with the foreign words that were listened to in the dream. The hippocampus, a brain structure essential to starvation associative learning, has also supported the recovery of sleep partnerships. The results of this experiment published open access in the scientific journal Current biology.
The active states of brain cells are essential for sleep learning
The research group of Katharina Henke examined whether a sleepy person is capable of forming new semantic associations between foreign words and translation words played during the active states of brain cells, so-called "Up-Up states." When we reach deep stages of sleep, our brain cells progressively coordinate their activity. During deep sleep, brain cells tend to be active for a brief period of time before they are articulated in a state of short inactivity. The active state is called "Current state" and the "Down status" inactive state. The two states alternate every half a second.
The semantic associations between sound words of artificial language and their German translation words were only coded and stored, if the second word of a pair was several times (2, 3 or 4 times) that was played during an ascending state. For example, when a sleeping person heard the words "tofer = key" and "guga = elephant", then after waking up they were able to classify with accuracy better than by chance if the foreign words touched by a dream were something big ("Guga") or small ("Tofer"). "It was interesting that the areas of language of the brain and the hippocampus, the essential memory core of the brain, were activated during the recuperation of the vocabulary learned from sleep because these brain structures usually mediate the learning of new vocabulary," says Marc Züst, first co-author of this article. "These brain structures seem to mediate the formation of memory regardless of the prevailing state of consciousness: unconscious during deep sleep, conscious during the wake."
The formation of memory requires no knowledge
In addition to its practical relevance, this new evidence for the learning of the dream challenges the current sleep theories and theories of memory. The notion of sleep as an encapsulated mental state, in which we separate ourselves from the physical environment, is no longer conservable. "We could refute that sophisticated learning is impossible during deep sleep," says Simon Ruch, co-author. The current results underline a new theoretical notion of the relationship between memory and consciousness that Katharina Henke published in 2010 (Nature Comments Neuroscience). "In how much and what consequences can be used, deep sleep for the acquisition of new information will be a matter of research in the coming years," says Katharina Henke.
The research group of Katharina Henke is part of Interfaculty Research Cooperation "Decoding Sleep: From Neurons to Health & Mind" (IRC). Decoding Sleep is a great interdisciplinary research project that is funded by the University of Bern, Switzerland. Thirteen research groups in medicine, biology, psychology and computer science are part of the IRC. The objective of these research groups is to better understand the mechanisms involved in sleep, consciousness and cognition.
The informed study was carried out in collaboration with Roland Wiest, who is affiliated with the Advanced Neuroimagen Support Center (SCAN) at the Institute for Interaction and Diagnostic Neuroradiology, Inselspital, of the University of Bern. The two research groups also belong to the BENESCO consortium, which consists of 22 interdisciplinary research groups specialized in sleep medicine, epilepsy and research on altered states of consciousness.
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