10/05/2010 11:33 pm ET Updated May 25, 2011

Memories Never Go Away, Study Suggests

Do We Ever Really Lose Our Memories?

That's what a research team at the Massachusetts Institute of Technology wanted to know. And so to begin, they genetically engineered some mice to develop Alzheimer's disease-like symptoms. The mice quickly forgot what had taken them several weeks to learn (one task was navigating a water maze).

The next phase involved sensory stimulation. Would it make a difference in memory retrieval? To find out, the researchers housed some of the rodents for a few more weeks in the equivalent of a Club Med for mice: a cage with a treadmill, climbing devices, tunnels and lots of colorful toys. Other genetically altered mice lived in traditional cages without the goodies.

What they observed was that the stimulated mice recovered their memories. The other mice did not.

Later, the scientists examined the brains of the enriched mice and found a surprise: New neurons had not replaced those that were destroyed. Rather, remaining neurons had compensated for those that were lost. In other words, even though specific brain cells were gone forever, their memories were still there.

Li-Huei Tsai, Ph.D. headed the team and concluded, "This recovery of long-term memory was really the most remarkable finding. It suggests that memories are not really erased in such disorders as Alzheimer's, but that they are rendered inaccessible and can be recovered."

And if memories can be recovered in Alzheimer's disease-like mice after enrichment, imagine what that might mean for people who are more mildly impaired. The implications are stunning and profoundly hopeful. (Source: L. Tsai, et al., "Recovery of Learning and Memory is Associated with Chromatin Remodeling," Nature 447 (2007):178-183).

Idelle Davidson is the co-author of "Your Brain After Chemo: A Practical Guide to Lifting the Fog and Getting Back Your Focus".