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Rats learn to navigate new spaces by replaying memories in reverse order, a study released in February suggests. After exploring an environment such as a maze, rats typically pause to eat, groom or rub their whiskers. Researchers had ignored such behavior because it seemed unimportant —rats being rats. But a pair of investigators from the Massachusetts Institute of Technology decided to see what the rat brain is doing during these interludes.
The team placed electrodes into a rat’s hippocampus to monitor so-called place neurons, which fire in a specific sequence as a rat navigates a path. Surprisingly, when various rats paused on completion of a run, the place neurons fired in reverse order from the firing that had occurred during navigation. This reverse replay occurred more frequently after walking through new mazes than familiar ones, implying that the technique plays a role in learning.
The phenomenon is likely to prove important in people, too, says M.I.T.’s David J. Foster. “There is a wealth of data from experiments in many species, including humans, showing that if learning trials are spaced out in time, they are more effective.” Reverse replay may explain why.