Running a weak electric current through the brains of sleeping student volunteers improved their performance on a word-recall task. Prior to sleep, the students memorized 46 word pairs and, on average, recalled 36.5 of them. After the electrically stimulated sleep, they improved their recall to 41.2 words, compared with just 39.5 words for the group that did not receive the jolt. The findings suggest that electrically stimulating the brain can exert a synchronizing effect on individual neurons and produce beneficial results. The researchers, who published their work online November 5 in Nature, are now investigating just how long the improvement might last and how deep sleep affects memory—for some reason, humans begin to lose the ability to sleep deeply around 40 years of age, at about the same time that memory begins to decline.