During sleep, the hippocampus, a brain region important in learning and memory, repeatedly "replays" brain activity from recent awake experiences. This replay process is believed to be important for memory consolidation.

University of Arizona researchers found much less brain activity during sleep indicating a "replay" of the previous day's learning in the brains of 11 older rats compared to the brains of 11 younger rats exposed to the same situation.

The study, published in The Journal of Neuroscience, found rats with the least replay activity also performed the worst in tests of spatial memory. Irrespective of the animal's age, the researchers found that animals who more faithfully replayed the sequence of neural activity recorded in the maze during sleep also performed better on the spatial memory task the next day.

"This is the first study to suggest that an animal's ability to perform a spatial memory task may be related to the brain's ability to perform memory consolidation during sleep," lead study author Carol Barnes said in a statement.