Jim Davies writes:

During this Olympics, I’ve been rooting for Kelleigh Ryan, who is on the women’s foil team. She’s from Ottawa, where I live. Whenever she scored a point, she’d emit a victory scream, probably feeling a rush of pleasure. Watching her on television, I did, too.

Getting better at something involves emotion. When we do well, we have good feelings—pride, pleasure, excitement—and these emotions help reinforce whatever behaviors we just engaged in. Similarly, the pain of failure makes recent behaviors less likely in the future. This is conditioning, and we’ve all experienced it—when we’re awake. But what about when we sleep?

Sleep reinforces memories. We know this because after half an hour of sleep, people can remember things better than when they spend half an hour doing something else, like watching TV. Studies of rats show that their brains rehearse running through mazes while they sleep, in a process known as sleep replay. Memory’s function is to store information that will be useful. Because of this, our mind prioritizes remembering some things over others. Studies have shown, for example, that it’s easier to remember things that are useful for survival. Might sleep similarly focus on things that are particularly good or bad for us, like food and dangerous animals, and ignore things that are irrelevant to our well-being, like the exact shape of a cloud?

A recent study by the University of Geneva’s Virginie Sterpenich and colleagues tried to find out. [Continue reading…]