Sleep, for some, can be an elusive activity which requires complete darkness and silence. When it comes to sounds, they may have far more to do with a good night’s sleep than previously thought.

A new study, published in the Journal of Neuroscience, suggests that one way the brain discriminates between safe and potentially harmful sounds is by reacting differently to familiar and unfamiliar voices.

The study involved 17 volunteers who slept overnight in a sleep laboratory with researchers from the University of Salzburg in Austria conducting the research.

Electrical activity monitored their brains whilst sleeping with recording used by electroencephalography (EEG).

Audio recordings were softly played throughout the night to determine how noise and sounds affected a person’s sleep.

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In the recordings, a voice read names out loud, including the volunteer’s own name and other names.

Sometimes the voice was a person familiar to them, such as their parent or partner, and sometimes it was an unfamiliar voice.

The researchers then looked for differences in the brain’s response when it came to familiar and unfamiliar voices.

They identified two brain responses that changed depending on the familiarity of the voice: K-complexes and micro-arousals.

A K-complex is a waveform that may be seen on an electroencephalogram and occurs during stage 2 of NREM sleep.

Micro-arousals are recurrent brief awakenings from sleep, often less than 15 seconds in duration.

The researchers found that unfamiliar voices triggered more K-complexes than familiar voices.

It suggests that sounds that could be more threatening are more likely to wake a person up, therefore, the brain must work harder to suppress them which in turn causes disturbed sleeping.

It was also found that unfamiliar voices triggered more micro-arousals than familiar voices. 

The findings add evidence to existing theories that explain how the human brain protects us from danger during sleep.

The results of this study suggest that the identity of a speaker is a potential cue pointing to danger: familiar speakers are deemed safe, while unfamiliar speakers could pose a threat.

If you struggle to get a good night’s sleep in a new environment like a hotel room, you now know why.

This is another reason why sleeping in front of the television doesn’t allow for a good night’s rest.

The solution? Switch off the outside and unfamiliar voices for a better night’s sleep.

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