June 25 (HealthDay News) -- Researchers at MIT have confirmed that sleep is essential for long-term storage of memories.

Their study showed that mice unable to "replay" their awake experiences while asleep remember them less well than mice who can perform this function. Scientists from the RIKEN-MIT Center for Neural Circuit Genetics at MITs Picower Institute for Learning and Memory report their findings in the June 24 issue of Neuron.

"Our work demonstrates the molecular link between post-experience sleep and the establishment of long-term memory of that experience," study author Susumu Tonegawa, Picower Professor of Biology and Neuroscience, said in a school news release. "Ours is the first study to demonstrate this link between memory replay and memory consolidation. The sleeping brain must replay experiences like video clips before they are transformed from short-term into long-term memories."

Researchers tested their theories by implanting electrodes in the brains of mice that were fed a special diet to disrupt their trisynaptic circuits. These circuits, found in the hippocampus, are now confirmed to play a crucial role in processing memories before they move on to other regions for storage.

While they were awake and running in a maze, the mice formed cells that fired in recognition of their newly learned task -- negotiating the maze. Those cells fired in similar sequences during their post-run sleep. Mice whose trisynaptic circuits functioned properly during sleep remembered the maze longer than those whose trisynaptic circuits were disabled, researchers reported.

"Our conclusion is that the trisynaptic pathway-mediated replay of the hippocampal memory sequence during sleep plays a crucial role in the formation of a long-term memory," said Tonegawa.

SOURCE: MIT News Office, news release, June 2009