October 5, 2005
A new analysis of a standard brain test may help predict dementia
Although Alzheimer's disease affects millions of people worldwide, there is no way to identify this devastating brain disease at its earliest stages when there still may be time to delay or even prevent the downward spiral into dementia. In research settings, scientists are using sophisticated tools like MRI and PET to distinguish characteristics of brain function and anatomy that indicate future problems, providing a sort of screening test for the brain.
Now a new study by a research group at NYU School of Medicine demonstrates that the earliest manifestations of Alzheimer's, when the first signs of memory loss appear, can be screened with a relatively inexpensive, painless, and easy-to-use tool called an EEG (electroencephalograph).
In the study, published in the upcoming on-line issue of the journal Neurobiology of Aging, the researchers demonstrate that a computer analysis of the EEG, which measures the brain's electrical activity, accurately predicted healthy people in their 60s and 70s who would develop dementia over the next 7 to 10 years. It also identified individuals who would remain virtually unchanged over the same time span. The EEGs were almost 95 percent accurate in identifying those who would decline cognitively and those who would not, according to the study.
"Our results suggest that quantitative analysis of the EEG is sensitive to the earliest signs of the dementing process," says Leslie S. Prichep, Ph.D., Associate Director of the Brain Research Laboratories of the Department of Psychiatry, who led the study. Some day she says it may be used as one of the tools to evaluate a person's propensity for developing Alzheimer's, the most common form of dementia affecting people over 65. But for now the results need to be replicated in and validated by much larger prospective studies before they can be applied to screen large populations.
It takes about 30 minutes to perform an EEG, which involves placing recording electrodes on the scalp. The test is perfomed with the patient seated comfortably. There are no injections and the scalp is not shaved.
The NYU researchers, led by Dr. Prichep and Roy John, Ph.D., Professor in the Department of Psychiatry, evaluated a group of 44 individuals between the ages of 64 and 79 who felt that their memories were faltering. These people enrolled voluntarily in a long-term study at NYU's Silberstein Aging and Dementia Research Center where they underwent a battery of neuropsychiatric and other tests, which revealed that their brain function was normal for their age.
At the beginning of the testing process each volunteer was also given a baseline EEG test at the Brain Research Laboratories at NYU School of Medicine. They were tested there several more times over the next 7 to 10 years. Over this period, 27 of the 44 subjects developed mild cognitive impairment or full-blown dementia, and 17 remained stable. Applying a mathematical algorhythm to the brain scans, Drs. Prichep and John showed that certain characteristics of the pattern of brain waves on the baseline EEG were associated with future cognitive deterioration.
To the untrained eye EEGs look like a confusing thicket of squiggly lines. But the lines are actually waves that have been described mathematically by their amplitude and frequency composition as a function of age, based on data collected over the last 30 years by Drs. Prichep and John. They and their NYU colleagues obtained this data from some 12,000 healthy people and psychiatric patients who had been given EEGs. About 3,500 of the EEGs were from aging and dementia patients.
"We probably have the largest electrophysiological database of this kind in the world," says Dr. Prichep. "Since we can compare each individual's quantitative EEG to age-expected normal values, we were able to describe which features reflected expected changes occurring with normal aging and which might be associated with future decline," she says.
A prominent feature associated with cognitive deterioration on the baseline EEG was a brain wave called theta, which was excessive in people who would eventually decline, according to the study. This band was particularly abnormal in the frontal regions, along the lateral regions and in the right posterior region of the brain in those people who went on to decline.
Another feature was a slowing in the mean frequency of the EEG, which is described in cycles per second. Yet another distinctive feature of those who decline was a change in the synchronization between the two sides of the brain. The source of the theta has been shown to be the hippocampus, a brain region demonstrated in imaging studies with MRI and PET to be impaired in dementia, notes Dr. Prichep.
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