How do sleeping people wake up?

Only certain noises wake sleepers

Munich - The brain actively defends its sleep against noise. If the sleeping person's hearing reports stimuli that differ slightly from the usual background noise, not only does the auditory cortex fail to react normally, other areas of the brain are even regulated downwards, as a study by the Max Planck Institute for Psychiatry in Munich has shown. The researchers involved consider this to be a protective mechanism designed to prevent sleepers from waking up.

Protective mechanism in sleep

In order to prevent one from waking up to every noise, the alarm antennae would be soothed, explains Philipp G. Sämann, one of the authors of the study: "In this dulled state we can keep up our sleep." The areas that are slowed down after a sound are usually responsible for alarm conditions or are involved in triggering movements.

The protective mechanism for sleep naturally only works for slightly different stimuli, explains the researcher. In the case of strong stimuli - for example, if your own name is called or the alarm clock goes off - you wake up anyway.

Different phases of attention

However, the brain does not stay in this subdued state all the time. According to Sämann, several times per minute there are so-called K-complexes for one to two seconds, in which the measured brain waves are strong. Sounds that are perceived during these phases lead to a reaction that is more similar to the reaction in the waking state than in the sleep. The attention is then higher. The brain is probably reassessing the stimuli - a kind of short test to check whether it is okay to go back to sleep.

For their investigation, the researchers measured the brain waves using electroencephalography (EEG) and recorded the brain using functional magnetic resonance imaging. This enabled them to compare the activation of individual areas while awake and asleep, before and after a sound. (APA / AP)