Students are told to “sleep on it,” because many experiments have shown an early stage of sleep helps consolidate the memory of recently learned facts. Now German neuroscientists have found that stimulating the sleeping brain with external electric fields can further boost memory performance.
Jan Born and his colleagues at the University of Luebeck gave a simple memory test—sets of word pairs—to 13 volunteer medical students and then let them fall asleep. As expected, their ability to remember the words improved after a nap. “Slow-wave sleep,” Born says, “has been suspected to be the phase of sleep when memory consolidation occurs.” During this phase, the brain generates waves of neuronal activity that oscillate from front to back, about once per second. But whereas memories of facts are known to solidify during this slow-wave period, the electrical oscillations themselves were not thought to be important to the process.