The brains of people with a genetic risk for Alzheimer's have to work harder than normal to perform simple memory tasks long before any outward symptoms of the disease develop, a study suggests.
The findings suggest that the measuring technique used in the study could develop into a kind of mental stress test for early detection of Alzheimer's, much like treadmill tests for heart abnormalities.
Zaven Khachaturian, former director of the Alzheimer's Research Office at the National Institutes of Health, said the study is exciting because it bolsters hope of identifying patients who could benefit from early drug treatment.
''There's something wrong already, but you can't see it clinically,'' he said.
The study was conducted by scientists at the University of California at Los Angeles and was published in Thursday's New England Journal of Medicine. They recruited 30 people ages 47 to 82, all of whom had tested normal on conventional memory tests.
They were checked for APOE E4 allele, a gene variant already known to be associated with Alzheimer's. Then, their brains were scanned with magnetic resonance imaging while they recalled words memorized from a list.
Those with the Alzheimer's gene produced scan signals that were about twice as strong and more widespread than those of other participants. The magnetic signals indicate greater blood flow - and thus greater mental effort - in regions of the brain near the temple and forehead, the researchers say.
Earlier research had implicated those areas in Alzheimer's.
In recent years, researchers have pinpointed metabolic brain deficiencies and other early markers that may foretell Alzheimer's. This study, though, is the first time that researchers have identified brain differences in at-risk people while they perform assigned mental tasks.
''The brains appeared to be compensating. The brains of people with the genetic risk have to work harder,'' said UCLA psychiatrist Dr. Gary Small, who led the research.
In its early results, his team tested 14 of the same people two years later. None was diagnosed with Alzheimer's, but those with the strongest signals two years earlier tended to lose the most memory ability.
''It has the potential to be a diagnostic tool,'' said Dr. Reisa Sperling, a neurologist at Brigham and Women's Hospital in Boston.
But scientists cautioned that patients must be studied for longer to be sure the test is picking up on early Alzheimer's, not just the normal effects of aging.
Anti-inflammatory and other drugs are now being tested to delay the onset of Alzheimer's symptoms. Scientists said early detection could be combined with such drug treatment, perhaps within several years.
About 4 million Americans, or about one in 10 people over age 65, struggle with the memory loss and other indignities of the mind-destroying disease. Former President Reagan has Alzheimer's.
Drugs can now relieve symptoms but not cure the disease.