The sleeping brain monitors and learns unfamiliar voices

A new study led by scientists at the University of Salzburg shows that the brain continues to selectively respond to environmental stimuli such as unfamiliar voices during sleep.

Researchers performed polysomnography recordings of male and female participants who were presented with either their own name or an unfamiliar name while sleeping at night and spoke in a familiar or unfamiliar voice. ..

“Our findings highlight discrepancies in the brain’s response to auditory stimuli, based on their relevance to sleepers,” the authors say.

Based on their observations, the authors argue that the sleeping brain enters a “sentinel processing mode”, during which time it maintains its ability to process important external sensory information while engaging in internal sleep processes. To do.

These new findings were published on January 17th. The Journal of Neuroscience “The brain selectively tunes to an unfamiliar voice during sleep.. “

Sleep and its neural mechanisms have confused both scientists for many years. New research shows that the human brain balances the need for sleep and awakening by screening the environment for unfamiliar voices.

Following previous studies showing that the brain continues to process sensory information during sleep, researchers are assessing the brain’s ability to extract and process sensory information related to sleep in current studies.

We are mainly interested in the total amount of sleep we get at night, but sleep occurs at a stage that can be distinguished by specific brain waves and neural activity. These include rapid eye movement (REM) sleep and non-rapid eye movement (NREM) sleep.

In this study, the research team detected K-complexes, sleep spindles, and microawakening, and evaluated event-related responses and phase synchronization between tests to various sensory stimuli during non-rem sleep.

The K complex is a characteristic waveform with a frequency of about 1 Hz and is found in brain waves during the second stage of non-rem sleep. They occur spontaneously or in response to sensory stimuli and are thought to result from the conflict between sensory activation and the effects of sleep protection.

“During non-rem sleep, unfamiliar voices induced more K-complexes and microawakening than familiar voices,” the authors say.

Researchers compared the stimuli that elicit the K complex and found that unfamiliar voices evoked greater and more synchronized brain responses and stronger forces at frequencies above 16 Hz compared to familiar voices. is showing. The authors also showed that there was no difference in brain response in the absence of the K complex.

“Our results suggest a crucial role for the K complex in the selective processing of relevant information during non-rem sleep,” the authors say.

Familiar voices also caused the K complex, but researchers observed that only those caused by unfamiliar voices were associated with large-scale changes in brain activity associated with sensory processing.

What the brain can still learn during sleep has been shown by the decrease in the brain’s response to unfamiliar voices as the night progresses and unfamiliar voices become more familiar.

“The decrease in the number of K complexes caused by unfamiliar voices in the second half compared to the first half of the night supports the idea that the sleeping brain continues to learn new information during sleep,” the author writes. increase.

New discoveries indicate the existence of a state in which the brain retains the ability to respond to relevant stimuli while maintaining the sleep process. The authors believe that the K complex allows the brain to enter this “sentinel processing mode”.