New research has established that mice dream and during their sleep there is a two-way dialog between the hippocampal recent day memory area and the neo-cortex that is believed to be involved in long-term memory.

The content of the mice dream is also no longer secret. In the sleep they are replaying the sequence of steps that they had executed in a maze, but in a reverse order, and in lesser time and in general are rehearsing the structure of the maze (the mouse trap). Learning, it is to be remembered, arises from these replays of fast rewinds and sleep it seems is necessary for learning.

Some quotes from the article:

During nondreaming sleep, the neurons of both the hippocampus and the neocortex replayed memories — in repeated simultaneous bursts of electrical activity — of a task the rat learned the previous day.

Earlier this year Dr. Wilson reported that after running a maze, rats would replay their route during idle moments, as if to consolidate the memory, although the replay, surprisingly, was in reverse order of travel. These fast rewinds lasted a small fraction of the actual time spent on the journey.
In the findings reported today, the M.I.T. researchers say they detected the same replays occurring in the neocortex as well as in the hippocampus as the rats slept.

The rewinds appeared as components of repeated cycles of neural activity, each of which lasted just under a second. Because the cycles in the hippocampus and neocortex were synchronized, they seemed to be part of a dialogue between the two regions.

Because the fast rewinds in the neocortex tended to occur fractionally sooner than their counterparts in the hippocampus, the dialogue is probably being initiated by the neocortex, and reflects a querying of the hippocampus’s raw memory data, Dr. Wilson said.

“The neocortex is essentially asking the hippocampus to replay events that contain a certain image, place or sound,” he said. “The neocortex is trying to make sense of what is going on in the hippocampus and to build models of the world, to understand how and why things happen.”

PS: My blog post has deliberately used words like ‘dream’, ‘mouse’ and ‘traps’ instead of the correct ‘sleep’, ‘rats’ and ‘mazes’: just to come up with a juicy headline!!

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