Awake mental replay of past experiences is essential for making informed choices, suggests a study in rats. Without it, the animals memory-based decision-making faltered, say scientists funded by the National Institutes of Health. The researchers blocked learning from, and acting on, past experience by selectively suppressing replay encoded as split-second bursts of neuronal activity in the memory hubs of rats performing a maze task.
"It appears to be these ripple-like bursts in electrical activity in the hippocampus that enable us to think about future possibilities based on past experiences and decide what to do," explained Loren Frank, Ph.D., of the University of California, San Francisco, a grantee of the NIH's National Institute of Mental Health (NIMH). "Similar patterns of hippocampus activity have been detected in humans during similar situations."
Frank, Shantanu Jadhav, Ph.D., and colleagues, report on their discovery online in the journal Science, Thursday, May 3, 2012.
"These results add to evidence that the brain encodes information not only in the amount of neuronal activity, but that its rhythm and synchronicity also play a crucial role," said Bettina Osborn, Ph.D., of the NIMH Division of Neuroscience and Basic Behavioral Science, which funded the research.
Frank and colleagues had discovered in previous studies that the rhythmic ripple-like activity in hippocampus coincided with awake mental replay of past experiences, which occurs during lulls in the rats' activity. The same signal during sleep is known to help consolidate memories. So the researchers hypothesized that these awake ripple states are required for memory-guided decision-making. To test this in the current study, they selectively suppressed the ripple activity without disturbing other functions, while monitoring any effects on the animals' performance in a maze task.
Individual neurons in certain areas of the hipp
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NIH/National Institute of Mental Health