The brain reacts strongly to foreign voices during sleep
Specifically, the reaction of sleeping people to such voices was examined. As the team reports in the “Journal of Neuroscience”, the brain reacts selectively and strongly to these stimuli during sleep – both in light sleep and in stable deep sleep.
We listen to the world around us even when we are asleep
Even during sleep, the brain selectively perceives acoustic stimuli. Manuel Schabus and his team from the Center for Cognitive Neuroscience (CCNS) at the University of Salzburg (Department of Psychology) have investigated how this is differentiated.
The scientists played the voices of acquaintances or life partners to 17 people during their night’s sleep – specifically in non-REM sleep phases in which they hardly dream – and recorded the reaction to voices from complete strangers. The first names of the respective subjects as well as other first names were spoken. During this, the brain activity of the participants was monitored with high-resolution 256-channel EEG (electroencephalography).
Special brainwaves from unknown voices
It was reported that unfamiliar voices trigger more so-called K-complexes than known ones. This is a special pattern of brainwaves associated with the acoustic stimuli associated with sleep while allowing the sleeper to continue sleep if the stimulus is presented as not too threatening. “Although familiar voices could also trigger K-complexes, only those from unfamiliar voices were associated with far-reaching changes in brain activity that indicate deeper sensory processing,” explains Schabus.
Familiar voices seem different
The longer the night lasts and the more familiar the initially unknown voice becomes, the less frequently these brain reactions occur. “This even suggests that the brain is able to learn completely new things or increasingly filter them out during sleep,” emphasizes Schabus.
Apparently, the K complexes allow the brain to enter a “sentinel” processing mode. In this state, it can deal with the internal processes that take place during sleep, but at the same time it is able to respond to relevant stimuli.
The brain is never completely at rest
The bottom line is that our brain is never completely quiet and inactive, but is always looking for relevant stimuli, and the best sleep is possible in familiar and familiar surroundings, according to the scientist.