Why can sleep salve the emotions?

“Sleep is pain’s easiest salve,” according to the English poet John Donne (1572-1631), and many of us will know how a good night’s slumber can help to calm heightened emotions.

But why can sleep soothe us so? Researchers from the University of California, Berkeley, have been looking at links between sleep and emotion, and their findings suggest that REM or “dreaming” sleep provides a sort of balm for emotional memories.

The study used an MRI scanner to measure brain activity in 35 participants as they viewed 150 emotional images.

Twelve hours later, they repeated the experiment, which was timed so that some participants had slept in between, while others hadn’t.

The findings, published recently in Current Biology, show that on the second viewing, those who had slept showed reduced activity in an area called the amygdala, which is linked with fear and emotion.

The researchers also tracked brain activity in participants as they slept and concluded that the physiology of REM sleep could weaken the responsiveness to previously viewed stimuli.

“We know that during REM sleep, there is a sharp decrease in levels of norepinephrine, a brain chemical associated with stress,” says researcher Matthew Walker in a statement. “By reprocessing previous emotional experiences in this neurochemically safe environment of low norepinephrine during REM sleep, we wake up the next day, and those experiences have been softened in their emotional strength. We feel better about them, we feel we can cope.”