Disturbed by something unpleasant? We all know it. Fortunately, that feeling will pass. A new day, a new beginning. At least:if you have peaceful REM sleep. Researchers at the Netherlands Brain Institute discovered why you will be more resistant tomorrow to what still upset you today. And why that can go wrong.
Something scary or annoying doesn't go unnoticed. The so-called limbic circuit of brain cells and connections is immediately active in our brain. With the amygdala at the front, a core located deep in the brain, which you could see as the siren of the brain:pay attention! In order to function properly, that siren must also be turned off again. Quiet REM sleep, the part of sleep with the most vivid dreams, appears to be essential for this.
The researchers placed their participants in an MRI scanner in the evening and offered them a specific scent while upsetting them. The brain scans showed how the amygdala was becoming active. The participants then spent the night in the sleep lab, while brain activity during sleep was measured with EEG, and the specific smell was occasionally offered again. The next morning, the researchers tried to upset their volunteers again, in exactly the same way they did the night before. That worked a lot less well. Brain circuits had adapted overnight, the siren of the brain no longer needed to sound. The amygdala reacted much less violently, especially in those who had much calmer REM sleep and who were also exposed to the specific smell.
However, the participants also included people with restless REM sleep. It was surprisingly different for them. Brain circuits hadn't adjusted properly overnight, the siren of the brain continued to sound the next morning. While offering the scent to people with restless REM sleep at night helped with processing, it was counterproductive for people with restless REM sleep.
During sleep, "memory traces" of experiences of the past day are played like a kind of movie. A specific memory trace can be recalled from all the day's remains by offering the scent again during the sleep that was associated with it during the day. Meanwhile, played memory tracks are modified:some connections between brain cells are strengthened, others weakened. These nighttime adaptations are essential for adjustment and recovery after an unpleasant experience and are disrupted by restless REM sleep.
