"This recovery of long-term memory was really the most remarkable finding," said Tsai. "It suggests that memories are not really erased in such disorders as Alzheimer's, but that they are rendered inaccessible and can be recovered."
When the researchers studied the brains of the animals that had been exposed to the extra stimuli, they found no evidence of increased growth or formation of new neurons when compared to brains of mice that had not experienced the enriched environment. However, they did find anatomical and biochemical evidence for growth of connections among neurons.
Tsai and her colleagues also sought to understand the biological mechanism by which environmental enrichment enhanced learning and memory in the mice. "Even though the learning-enhancement effects of environmental enrichment have been known for half a century, nobody really knows the mechanism behind it," said Tsai. "However, there has also been a growing body of evidence that chromatin remodeling has a beneficial effect on learning and memory," she said.
Chromatin is found in the nuclei of cells. It is composed of DNA spooled around bundles of histone proteins. The addition of small chemical tags to known as acetyl of methyl groups to the histones can alter the way chromatin is organized, which in turn determines which genes are turned on. Indeed, when Tsai and her colleagues analyzed the histones of enriched mice versus non-enriched animals, they found that environmental enrichment induced histone modification in the enriched mice.
Tsai and her colleague
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Contact: Jennifer Michalowski
michalow@hhmi.org
301-215-8576
Howard Hughes Medical Institute
29-Apr-2007