The memories destroyed by Alzheimer’s disease and other types of dementia could be restored by therapy, research has suggested.

Experiments on mice have indicated that long-term memories that appeared to have been lost to degenerative brain diseases can be recovered when the animals are given a promising form of treatment.

The research raises the prospect that treatments for Alzheimer’s and similar conditions might eventually not only stop patients’ mental decline, but reverse damage that has already taken place.

It had generally been thought that memory loss caused by dementia was permanent, and that the best that could be hoped for would be drugs and therapies that prevented any further deterioration.

The study, led by Li-Huei Tsai of the Massachusetts Institute of Technology, shows that these memories may not have been erased completely. Instead, damage to the brain may be interfering with Alzheimer’s patients’ ability to retrieve and use them.

“The memories are still there, but they are rendered inaccessible by neural degeneration,” Dr Tsai said. “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.”

The research, using mice genetically engineered to suffer a neurodegenerative disease similar to Alzheimer’s, also raises hope that two approaches to treatment might be effective.

Dr Tsai’s team found that enriching the environment of the mice, with treadmills for exercise and colourful toys of many different textures, significantly improved learning and memory, and appeared to build new connections between nerve cells in the brain.

This accords with evidence from humans that exercise and mental stimulation, such as learning languages or doing crosswords or Su Doku puzzles, appear to have a protective effect.

Similar results were also achieved by giving the mice a drug known as an HDAC inhibitor, which promotes nerve cell growth. Much more work is needed before this can be tested in people, but scientists said that it was a promising lead.

The researchers determined that both treatments can revive lost memories by comparing mice before and after a gene was activated to cause neuro

logical decline. The mice were first conditioned to fear entering a chamber, by giving them a mild electric shock whenever they did so. The animals also learned to find a submerged platform in murky water.

When a gene called p25 was activated, the mice developed symptoms like those of Alzheimer’s disease, and forgot both that they were afraid of the electric-shock chamber and the ability to find the platform.

After receiving the environmental enrichment or the drug therapy, the mice recovered these lost memories.

Details of the research are published in the journal Nature.

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