The Brain Pays Attention to Unfamiliar Voices During Sleep

Summary: During deep sleep, the presence of an unfamiliar voice elicits more K-complexes, a type of brain wave linked to sensory perturbances during sleep, compared to the sound of a familiar voice.

Source: SfN

A good night’s sleep is not as simple as it appears. While you snooze, your brain continues to monitor the environment, balancing the need to protect sleep with the need to wake up.

One example of how the brain accomplishes this is by selectively responding to unfamiliar voices over familiar ones, according to new research published in Journal of Neuroscience.

Researchers at the University of Salzburg measured the brain activity of sleeping adults in response to familiar and unfamiliar voices.

Unfamiliar voices elicited more K-complexes, a type of brain wave linked to sensory perturbances during sleep, compared to familiar voices.

This shows a sleeping woman
The ability allows the brain to balance sleep with responding to environmental cues. Image is in the public domain

While familiar voices can also trigger K-complexes, only those triggered by unfamiliar voices are accompanied by large-scale changes in brain activity linked to sensory processing.

Brain responses to the unfamiliar voice occurred less often as the night went on and the voice became more familiar, indicating the brain may still be able to learn during sleep.

These results suggest K-complexes allow the brain to enter a “sentinel processing mode,” where the brain stays asleep but retains the ability to respond to relevant stimuli.

About this sleep and attention research news

Author: Calli McMurray
Source: SfN
Contact: Calli McMurray – SfN
Image: The image is in the public domain

Original Research: Closed access.
The brain selectively tunes to unfamiliar voices during sleep” by Mohamed S. Ameen, Dominik PJ Heib, Christine Blume and Manuel Schabus. Journal of Neuroscience


The brain selectively tunes to unfamiliar voices during sleep

The brain continues to respond selectively to environmental stimuli during sleep. However, the functional role of such responses, and whether they reflect information processing or rather sensory inhibition is not fully understood.

Here, we present 17 human sleepers (14 females) with their own name and two unfamiliar first names, spoken by either a familiar voice (FV) or an unfamiliar voice (UFV), while recording polysomnography during a full night’s sleep. We detect K-complexes, sleep spindles, and micro-arousals, and assess event-related, and frequency responses as well as inter-trial phase synchronization to the different stimuli presented during non-rapid eye movement (NREM) sleep.

We show that UFVs evoke more K-complexes and micro-arousals than FVs. When both stimuli evoke a K-complex, we observe larger evoked potentials, more precise time-locking of brain responses in the delta band (1-4 Hz), and stronger activity in the high frequency (>16Hz) range, in response to UFVs relative to FVs. Crucially, these differences in brain responses disappear completely when no K-complexes are evoked by the auditory stimuli.

Our findings highlight discrepancies in brain responses to auditory stimuli based on their relevance to the sleeper and propose a key role for K-complexes in the modulation of sensory processing during sleep. We argue that such content-specific, dynamic reactivity to external sensory information enables the brain to enter a ‘sentinel processing mode’ in which it engages in the important internal processes that are ongoing during sleep while still maintaining the ability to process vital external sensory information.

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