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About two years ago, 29 people visited a neuroscience lab in the Netherlands to sing karaoke. Wearing muffled headphones so they could hear the music but not their own voices, it was almost inevitable that they would sing “Silent Night” or the Dutch national anthem out of tune.
Dutch researchers recorded each individual sing, then played the recording back to him or her. Listening to themselves sing solo evoked feelings of shame and embarrassment and sparked higher-than-normal activity in the subjects’ amygdalae. Fortunately for some study participants, a good night’s sleep was enough to lessen the amygdala’s response when they listened to the recording again the next day. But others who had experienced restless sleep—specifically poor-quality REM, or rapid eye movement, sleep—experienced the opposite: their amygdalae were just as sensitive, if not more, to the recording the next day.
The findings suggest that poor-quality REM sleep ...