Direct evidence of role of sleep in memory formation is uncovered

It's been known for more than a century that sleep somehow is important for learning and memory. Sigmund Freud further suspected that what we learned during the day was "rehearsed" by the brain during dreaming, allowing memories to form. And while much recent research has focused on the correlative links between the hippocampus and memory consolidation, what had not been identified was the specific processes that cause long-term memories to form.

As posted online September 11, 2009 by Nature Neuroscience, György Buzsaki, professor at the Center for Molecular and Behavioral Neuroscience at Rutgers University, Newark, and his co-researchers, Gabrielle Girardeau, Karim Benchenane, Sidney I. Wiener and Michaël B. Zugaro of the Collége de France, have determined that short transient brain events, called "sharp wave ripples," are responsible for consolidating memory and transferring the learned information from the hippocampus to the neocortex, where long-term memories are stored.

Sharp wave ripples are intense, compressed oscillations that occur in the hippocampus when the hippocampus is working "off-line," most often during stage four sleep, which, along with stage three, is the deepest level of sleep.