A group of scientists at the University of Heidelberg in Germany provided the first clues. Specific cells in the hippocampus — that region involved in storing memories — fired when mice slept, the scientists found. But the cells didn’t fire normally. Instead, electrical signals spontaneously fired near the middle of an axon, then traveled back in the direction of the cell body. In other words, the cells fired in reverse.
This boosted learning. It did so by making connections between cells stronger. Again, the action sort of wired together the cells. Research by Olena Bukalo and Doug Fields showed how it happens. They are neuroscientists at the National Institutes of Child Health and Human Development in Bethesda, Md.