By Merritt McKinney

NEW YORK (Reuters Health) - Older people who have a normal memory but are genetically at risk of Alzheimer's disease have to kick their brains into overdrive to perform the same memory tasks as others who are not at risk of the disease, according to results of a new study.

The test used to measure brain activity in the study may help identify people at risk of Alzheimer's, the study's lead author told Reuters Health in an interview.

``People with a genetic risk for Alzheimer's have to use their brains more to perform memory tasks than people who don't have that genetic risk,'' said Dr. Gary W. Small, of the University of California, Los Angeles. He explained that the activity was greatest in areas of the brain that are eventually affected by Alzheimer's disease.

And the brain scan was a good predictor of a person's memory a couple of years later, when some of the participants were retested, according to Small. ``We saw that the people who had greater brain activation during a memory task were the ones that had worse memory performance 2 years later,'' he said.

Small and his colleagues based the findings on 30 people aged 47 to 82 who did not have any memory problems, including 16 who had a genetic variation known as APOE-e4, which is linked to an increased risk of Alzheimer's disease. There are three different APOE genes--e2, e3 and e4--people with one or two copies of APOE-e4 (from one or both parents) are at greater risk than those with a different combination of the genes.

In the study, all participants underwent a brain scan called functional magnetic resonance imaging while performing a series of memory tests. The results of the study are published in the August 17th issue of The New England Journal of Medicine.

It may seem odd that increased brain activity may signal a risk for memory loss, but Small said that the phenomenon makes sense. He likened the bran scan to a cardiac stress test, during which a person's heart is monitored during exercise. Just as the heart of a person with heart disease has to work harder than that of an athlete during exercise, the brain of a person at risk of Alzheimer's appears to have to work harder to perform the same task as someone who is not at risk, according to Small.

The researcher explained that not everyone with a genetic risk factor for Alzheimer's will develop the disease, since it is caused by a combination of genetic and environmental factors. However, measurements of brain activity, along with other tests, may help identify people at risk of developing the disease, Small and his colleagues note.

The findings may help identify good candidates for clinical trials of drugs designed to slow down or stop the progression of Alzheimer's disease, Dr. Ingmar Skoog, of Sahlgrenska University Hospital in Sweden, writes in an accompanying editorial. The test may also be used to see how well such drugs work, Skoog notes.

　　(From Yahoo)