When we hear unknown voices in the middle of the night, it stimulates our brain activity.
- Our nights are punctuated by three phases: light slow sleep, deep slow sleep and paradoxical sleep.
- These three phases form a sleep cycle, lasting approximately 90 minutes.
- During each of them, the brain remains active.
Our brain never sleeps. At night, it sorts all the information received during the day, certain neurons are activated to plunge us into specific sleep phases. Thus, it acts as a control tower, whose activity never ceases, and which would be able to alert us to any abnormal signal. This is explained by researchers in JNeurosci. During our sleep, brain activity intensifies in the event of an unknown noise.
Changes in brain activity
These scientists from the University of Salzburg, Germany, measured the brain activity of 17 sleeping adults. The study took place over two days: the first night aimed to put the participants at ease, and the experiment started on the second. While they slept, the scientists played recordings of known and unknown voices speaking their names and unknown first names. The sound level was low enough that it didn’t wake them up. Unfamiliar voices elicited more K-complexes, a type of brain wave linked to sensory disturbances during sleep, compared to familiar voices. These can also generate K-complexes, but those triggered by unfamiliar voices are accompanied by large-scale changes in brain activity.
An internal alarm
As the night progressed, and as the snippets aired, brain responses to the unfamiliar voice occurred less often. In sum, the voice has become more familiar, showing that the brain may still be able to learn during sleep. According to the authors, these results prove that K-complexes allow the brain to enter a “sentinel treatment mode“, where the brain remains dormant but retains the ability to respond to stimuli. The organ continues to perform these internal tasks, but at the same time it is able to react in the event of new information.”Unknown voices should not speak to us at night, explains Manuel Schabus, one of the authors of this research. This triggers an alarm in the brain.“He adds that this process could explain why we sometimes have trouble sleeping in novel environments, such as hotel rooms.
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