Have you ever seen a duck sleep and wondered how it keeps one eye open? Ducks, like many other birds, sleep with half their brains awake while the other half sleeps. This is called “unihemispheric sleep” and allows the animal to monitor the environment for predators while getting the rest it needs.
Advances in sleep science show that the human brain also monitors its environment During the dream. Since our eyes are closed, this monitoring must be based primarily on hearing.
The sleeping brain faces a difficult balancing act. To protect sleep, you have to suppress harmless sounds, like your partner being late or the sound of raindrops hitting the roof. But it has to be ready to wake you up if a potentially dangerous noise sounds.
A new study, published in the Journal of Neuroscience, suggests that a way in which the brain discriminates between safe and potentially harmful sounds. harmful is reacting differently if you hear familiar voices or if you hear unfamiliar voices.
Researchers from the University of Salzburg (Austria) recruited 17 volunteers who slept overnight in a sleep laboratory. While they slept, the electrical activity of their brains was recorded using electroencephalography (EEG).
Throughout the night, the researchers played the audio recordings of the sleeping volunteers softly enough so as not to wake them up.
In the recordings, a voice read names aloud, including the volunteer’s own name and other names. Sometimes the voice was a familiar person, such as their parent or partner, and other times it was an unfamiliar voice.
Researchers looked for differences in the brain’s response to familiar and unfamiliar voices. unknown voices. They identified two brain responses that changed depending on the familiarity of the voice: K-complexes and micro-arousals.
K-complexes are sharp waves seen on sleep EEG and last about half a second. The brain can generate them spontaneously, but most often they occur after an external disturbance, such as someone gently touching you while you sleep. They are believed to protect sleep by preventing you from waking up if the disturbance is likely to be harmless.
The researchers found that unfamiliar voices triggered more K complexes than familiar voices. They suggest that sounds that could be more threatening are more likely to wake a sleeping person, so the brain has to work harder to suppress them.
Interestingly, in K complexes the difference between familiar and unknown voices he disappeared in the second half of the night. This may reflect the brain’s learning that the unfamiliar voice is safe.
Unknown voices also triggered more microarousals than familiar voices. Microarousals are a normal part of sleep and appear on EEG as a brief combination of brain activity similar to that of wakefulness and sleep.
Like K complexes, they can occur spontaneously or after an external disturbance . They can last several seconds, but usually do not cause the person to wake up.
The role of microexcitations is not well understood. Previous research has indicated that they may play a role in processing information from the environment to determine whether or not it might be harmful.
What does all this mean?
Although this is a small study, the findings add evidence to the existing theories that explain how the human brain protects us from danger during sleep.
Scientists have previously proposed that the brain enters a “sentinel processing mode” or a “standby mode” while we sleep .
This means that the brain continues to monitor events in the environment, even when consciousness fades as we fall deeper asleep.
Incoming information is processes to decide if it is relevant and dangerous. According to this evaluation, the brain protects sleep or wakes us up.
The results of this study suggest that a speaker’s identity is a potential signal that points to danger: familiar speakers are considered safe, while that unknown speakers could pose a threat. The evolutionary benefits are easy to see.
But it is difficult to demonstrate that the increase in K complexes and microexcitations in response to unknown voices represent the brain making a judgment about possible danger. It could also just be that the new voices get more attention.
If you’re having trouble getting a good night’s sleep in a new environment like a hotel room, now you know why. Like the duck with its one eye open, your sleeping brain is busy getting used to its new surroundings, firing off more K-complexes and microarousals than usual.
But he is also learning about the medium environment and will soon adapt. You can help by pressing the stop button on that podcast or TV show and letting yourself fall asleep enjoying the safety that lies in silence.
*Jakke Tamminen is Professor of Psychology at the Royal University Holloway of London.
This item is originally published on The Conversation and is published on BBC Mundo under a Creative Commons license. You can read the original version here.
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