Danger! Danger!

While we may be unconscious during sleep, our brains stay on alert for danger. That’s the finding of a study published in the January issue of The Journal of Neuroscience. 

Subjects of the study were observed in a sleep lab while they underwent polysomnography to record their brain waves, oxygen levels, heart and breathing rates, and movements. 

“We presented the participants with audios of their own names and two unfamiliar names. These names were spoken by either a familiar voice or an unfamiliar voice,” cognitive neuroscientist and study author Mohamed Ameen explained on Twitter.

Participants who were exposed to unfamiliar voices played softly exhibited a greater response than those who did not hear the voices. These responses included micro-arousals — brief moments of awakelike brain activity that last seconds. The function of micro-arousals isn’t yet totally understood. 

While both familiar and unfamiliar voices triggered brainwave patterns called K-complexes, only participants who heard unfamiliar voices experienced larger changes in brain activity related to sensory processing. K-complexes are thought to prevent humans from waking in response to harmless disturbances.

“K-complexes may be the key mechanism shaping how we sleep, helping the brain decide if we should stay asleep or wake up,” University of Salzburg cognitive neuroscientist Manuel Schabus told Inside Science. “It’s quite a smart mechanism that allows you to filter what’s relevant or not, and when it is relevant, it will trigger a chain of processes facilitating the processing of that information without needing you to wake up and disrupt sleep.”

Together, these findings suggest “the sleeping brain extracts relevant sensory information for further processing,” Ameen said.

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