To sleep is not only to dream, it's also when the brain gets busy setting the connections for memory formation. In his research conducted with collaborators at the Collége de France, Rutgers neuroscientist György Buzsaki has uncovered that compressed oscillations in the hippocampus, known as "sharp wave ripples," are responsible for forming long-term memories while we sleep.
It's been known for more than a century that sleep is somehow important for learning and memory, but what remained elusive was the specific process that causes long-term memories to form. As reported in Nature Neuroscience (September 13, 2009), Buzaski and his research team determined that sharp wave ripples are responsible for consolidating memory and transferring 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 with stage three is the deepest level of sleep.
During stage four sleep, Buzsaki explains, "it's as if many instruments and members of the orchestra come together to generate a loud sound, a sound so loud that it is heard by wide areas of the neocortex. These sharp, 'loud' transient events occur hundreds to thousands of times during sleep and 'teach' the neocortex to establish a long-term form of the memory, a process referred to as memory consolidation." The intensity and multiple occurrence of those ripples also explain why certain events may only take place once in the waking state and yet can be remembered for a lifetime, adds Buzsaki.
The researchers were able to pinpoint that sharp wave ripples are the cause behind memory formation by eliminating those ripple events in rats during sleep. The rats were trained in a spatial navigation task and then allowed to sleep after each session. Those rats that selectively had all ripple events eliminated by electrical stimulation were impeded in their ability to learn from the training, as compressed information was unable to leave the hippocampus and transfer to the neocortex.
"This is the first example that if a well-defined pattern of activity in the brain is reliably and selectively eliminated, it results in memory deficit; a demonstration that this specific brain pattern is the cause behind long-term memory formation," says Buzsaki.
The research also represents a move toward a new direction in neuroscience research. While previous research largely has focused on correlating behavior with specific brain events, researchers such as Buzsaki are increasingly challenging those correlations as they seek to identify the specific processes that cause certain events and behaviors to take place.
György Buzsaki, Rutgers Board of Governors Professor of Neuroscience, is recognized worldwide for his work in expanding the boundaries of scientific understanding about the brain's ability to process and store information. At the Center for Molecular and Behavioral Neuroscience at Rutgers University in Newark, he has focused on the hippocampus and the role of neurons located there in maintaining long-term memory, as well as related research into epilepsy, depression, schizophrenia and Parkinson's disease.
Buzsaki has won widespread international acclaim for his work, including the prestigious $ 2011 European Brain Prize, awarded by the Grete Lundbeck European Brain Research Foundation, for groundbreaking research into how human memory works. In addition, he was named ISIHighlyCited (top 250 most cited neuroscientist) in 2004; a Fellow in the American Association for the Advancement of Science in 2004; and Collége de France Distinguished Professor in 1998. He was presented with the Pierre Gloor Award from the American Clinical Neurophysiology Society in 1997, is an honorary member of the Hungarian Academy of Sciences, and sits on the editorial boards of several leading neuroscience journals.
He has had more than 200 peer-reviewed papers published in leading journals such as Science and Nature, many of which are among the most frequently cited by fellow scientists. The excellence and innovation of his research have been recognized by his peers, who awarded him one of neuroscience's most prestigious honors, the Krieg Cortical Discover Award in 2001. For more information about Buzsaki's research, visit http://osiris.rutgers.edu/frontmid/indexmid.html
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