Researchers have uncovered new evidence that sleep improves the brain's ability to remember information. Their findings demonstrate that memories of recently learned word pairs are improved if sleep intervenes between learning and testing and that this benefit is most pronounced when memory is challenged by competing information. The findings are reported in the July 12th issue of Current Biology by Jeffrey Ellenbogen, of Harvard Medical School, and his colleagues.
Whether sleep facilitates memory consolidation is a question as old as the experimental study of memory itself. In recent years, there has been a resurgence of experiments exploring this relationship. Although there is near-consensus that sleep promotes learning of certain types of perceptual memories (for example, learning to tap numeric sequences on a keyboard), there is ongoing debate about whether sleep benefits so-called declarative memory, a key type of memory that is based in the brain's hippocampus.
In the new work, the researchers studied the influence of sleep on declarative memory in healthy, college-aged adults. The results demonstrated a robust effect: Compared to participants who did not sleep during the trials, those who slept between learning and testing were able to recall more of the original words they had learned earlier. The beneficial influence of sleep was particularly marked when participants were presented with the challenge of "interference"--competing word-pair information--just prior to testing. A follow-up group further demonstrated that this sleep benefit for memory persists over the subsequent waking day. This work clarifies and extends previous study of sleep and memory by demonstrating that sleep does not just passively and transiently protect memories; rather, sleep plays an active role in memory consolidation.