July 15, 2015

Scientists 'Watch' Rats String Memories Together

Experiments show neurons firing as rats plan their next move

(July 15, 2015)  By using electrode implants to track nerve cells firing in the brains of rats as they plan where to go next, Johns Hopkins scientists say they have learned that the mammalian brain likely reconstructs memories in a way more like jumping across stepping stones than walking across a bridge. A summary of their experiments, published in the journal Science on July 10, sheds light on what memories are and how they form, and gives clues about how the system can fail.

“My own introspective experience of memory tends to be one of discrete snapshots strung together, as opposed to a continuous video recording,” says David Foster, Ph.D., an assistant professor of neuroscience at the Johns Hopkins University School of Medicine. “Our data from rats suggest that our memories are actually organized that way, with one network of neurons responsible for the snapshots and another responsible for the string that connects them.”

Foster and his team focused their experiments on a group of nerve cells in the hippocampus of the brain known — in animals and people — for creating a mental “map” of experiences, or memories. The cells are called place cells because they each develop a preferred place in an environment and mainly fire only when the animal is in that place.

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