SLEEPING minds: prepare to be hacked. For the first time, conscious memories have been implanted into the minds of mice while they sleep. The same technique could one day be used to alter memories in people who have undergone traumatic events. When we sleep, our brain replays the day's activities. The pattern of brain activity exhibited by mice when they explore a new area during the day, for example, will reappear, speeded up, while the animal sleeps. This is thought to be the brain practising an activity – an essential part of learning. People who miss out on sleep do not learn as well as those who get a good night's rest, and when the replay process is disrupted in mice, so too is their ability to remember what they learned the previous day. Karim Benchenane and his colleagues at the Industrial Physics and Chemistry Higher Educational Institution in Paris, France, hijacked this process to create new memories in sleeping mice (Nature Neuroscience). The team targeted the rodents' place cells – neurons that fire in response to being in or thinking about a specific place. These cells are thought to help us form internal maps; last year their discoverers won a Nobel prize. More via New Scientist.