A research team has found that, at least in mice, the brain processes new and old memories in separate phases of sleep, which might prevent mixing between the two. Assuming that the finding is confirmed in other animals, 'I put all my money that this segregation will also occur in humans', says Gyorgy Buzsaki, a systems neuroscientist at New York University in New York City. That's because memory is an evolutionarily ancient system, says Buzsaki, who was not part of the research team but once supervised the work of some of its members. Scientists have long known that, during sleep, the brain 'replays' recent experiences: the same neurons involved in an experience fire in the same order. This mechanism helps to solidify the experience as a memory and prepare it for long-term storage. To study brain function during sleep, the research team exploited a quirk of mice: their eyes are partially open during some stages of slumber. The team monitored one eye in each mouse as it slept....
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