The brain when asleep is more active when it hears unfamiliar voices than when it hears ones it recognizes. In a sleep lab in Austria, Manuel Schabus and his team watched 17 people, with an average age of 23, for two nights. They looked at how they slept and how they woke up. Schabus says that the first night was calm so that the subjects could get used to their new surroundings. The test was then set up so that the person who was sleeping either didn’t know who the voice came from or it came from a person they knew, like a parent or a romantic partner.
The researchers found that the sleepers’ brains were more active when they heard unfamiliar voices than when they heard familiar voices.
A type of brainwave called K-complexes – which is slow and isolated – rose in number when people heard new voices. Schabus says that K-complexes are interesting because they show how the body reacts right away to a change in the environment.
Schabus says it makes sense that people evolved to be more active when they heard new voices than when they heard familiar ones. “Unfamiliar voices should not be speaking to you at night – it sets off an alarm,” he says. It might be one reason why we have trouble sleeping in new places, like hotel rooms, says Schabus. Julie Darbyshire, a researcher at the University of Oxford, says that this study shows that people who hear new voices while they are sleeping are more disturbed than people who hear familiar voices.
Patients will also be surrounded by equipment that makes strange sounds like pings, bongs, and beeps. Unknown voices also caused fewer K-complexes in the second half of the night than in the first half. “’It means we can learn something new in the near-conscious state,” says Schabus.
