Studies What happens during sleep with the brain?

Synaptic changes decrypted during sleep
Why do we need sleep and what happens during the resting phases in our brain? Questions that can not be answered clearly until today. Researchers at the University Hospital Freiburg have now found out how the brain creates space for new information during sleep.

Why people and animals sleep, according to the Freiburg University Hospital "is still not clear." The research team led by Professor. However, Christoph Nissen, Head of the Sleep Laboratory at the Department of Psychiatry and Psychotherapy at Freiburg University Hospital, has shown in his current study that "in sleep, the general activity of nerve cell connections known as synapses is reduced." The brain virtually clears the sleeping space This creates new space for storing information. Their results have the researchers in the journal "Nature Communications".

During sleep, the activity of most synapses decreases and space for new information is created. (Image: Sagittaria / fotolia.com)

Activity of the synapses examined
As part of their study, the researchers first examined the general activity of the synapses in the brain, which is also referred to as total connection strength. For this purpose, a certain area in the brain, which is responsible for controlling a thumb muscle, was stimulated with the aid of a magnetic coil above the subject's head. Through this so-called transcranial magnetic stimulation (TMS), the connection strength could be checked. Here, the researchers found that after sleep deprivation already a significantly weaker stimulus triggers a contraction of the muscle. This is a sign of a higher synaptic connection strength.

Synaptic total strength increases during the day and decreases during sleep
Using electroencephalography measurements (EEG), the researchers also evaluated the different frequencies of the brain waves. Sleep deprivation has led to a significant increase in the so-called theta waves, reports the Freiburg University Hospital. From previous animal and human studies is known that this is another indication of increased synaptic total strength. According to Professor Nissen, "sleep decreases the increased total strength of synapses in the brain during the day", while "after sleep deprivation the activity remains at a high level".

Synaptic plasticity important basis of learning
In the course of sleep, most synaptic connections are weakened, some even completely degraded, the scientists report. Only important synapses would persist or even be strengthened. In this way, the brain creates space again to store new information. This adaptability is called synaptic plasticity and is an important basis for learning and flexible information processing. According to the research, the degradation also saves "space and save energy, since both are needed in the brain to a large extent by the connection points."

Lack of sleep leads to a state of satiety
When information is collected during the day, synapses in the brain are strengthened or newly created. In the current study, for the first time, it was possible to prove "that sleep downshifts the synapses again and thus creates room for new information", says study leader Prof. Dr. med. Nissen. "So the brain cleans up in sleep," emphasizes the expert. If this process is prevented by lack of sleep, the brain gets into a state of saturation. "Synapses can then no longer be sufficiently strengthened or rebuilt. Learning and flexible information processing are correspondingly difficult, "Nissen continues.

Protection against overloading
In their research, the researchers also found that the human organism has protection against overcharging. For the first time, indications for a principle have been discovered in humans, "which ensures a lasting stimulus processing, the so-called homeostatic plasticity", so the message of the Freiburg University Hospital. If the synapses are already maximally active due to long awake phases, new stimuli or information do not lead to a strengthening, but to a weakening of the nerve cell connections, report the researchers. New incoming stimuli would then be processed normally again. "It can be assumed that practically all the functions of the brain are influenced by it, such as emotion regulation, concentration or learning," says Prof. Nissen.

Why do some people sleep better sleep better?
According to the University Hospital Freiburg, the researchers "continue to find evidence that the growth factor BDNF (brain derived neurotrophic factor) plays an important role in the regulation of synaptic activity." Although it is known that BDNF after normal sleep, the rejoining of nerve cells and thus encouraging learning, but persistently high levels of BDNF in the blood during sleep deprivation have more likely led to synaptic saturation. "That could explain why some people cope better with sleep deprivation than others," says study director Prof. Nissen.

Hope for new therapeutic approaches
The researchers hope that their findings can also contribute to the development of new therapeutic options, for example after a stroke or depressive disorders. In these diseases, it is important to change the interconnections in the brain. "This could be a targeted influence on sleep-wake behavior, but also other methods such as transcranial direct current stimulation or drugs with new mechanisms of action on plasticity can be used," said the University of Freiburg. (Fp)