Scientists from Rutgers University and Collége de France, Paris have finally shown why sleep is an important part of complex memory formation. In Nature Neuroscience they are reporting that “sharp wave ripples,” short lasting brain events in the hippocampus when the brain is typically sleeping, combine and send the information from the hippocampus to the neocortex for long term storage.
During stage four sleep, Buzsaki [György Buzsaki, professor at the Center for Molecular and Behavioral Neuroscience at Rutgers University –ed.] 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 form 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.
Identification of a specific brain pattern responsible for strengthening learned information could facilitate applied research for more effective treatment of memory disorders.
“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 through electroencephalogram, neuronal spiking and functional magnetic resonance imaging studies, increasingly researchers are challenging those correlations as they seek to identify the specific process or processes that cause certain events and behaviors to take place.
Link: Rutgers Research: Direct Evidence of the Role of Sleep in Memory Formation is Uncovered…
Abstract in Nature Neuroscience: Selective suppression of hippocampal ripples impairs spatial memory