Scientists at Albert Einstein College of Medicine of Yeshiva University say that developing strategies to improve the prediction and diagnosis of dementia has critical therapeutic and public health implications.
"Typically, when neuropsychological tests are used for diagnostic purposes, an individual's level of performance on specific tests is measured against healthy individuals to determine cognitive impairment," says Dr. Roee Holtzer, assistant professor of neurology and psychology at Einstein and lead author of the study.
"However, this approach does not take into account intra-individual variability in cognitive function," he adds.
A research article in the journal JAMA says that intra-individual variability refers to inconsistency in performance measured in the same person.
During the study, the researchers evaluated 897 individuals, age 70 or older, who had taken part in The Einstein Aging Study, a longitudinal study of aging and dementia in Bronx, New York.
The subjects had follow-up visits every 12 to 18 months, during which they underwent detailed neurological and neuropsychological evaluations.
Dr. Holtzer revealed that he and his colleagues included tests for verbal IQ, attention/executive function, and memory.
He said that his team focused on whether within-person variability across several neuropsychological tests, assessed at the initial study visit, predicted future dementia.
"We know that level of performance on tests of memory, attention and executive function predicts dementia. However, this study showed for the first time that the degree of variability in performance across neuropsychological tests, measured within a person, improved the prediction of dementia above and beyond one's level of performance on each test alone," says Dr. Holtzer.
The subjects underwent extensive neurological and neuropsychological testing in the follow-up trials, in order to determine whether they remained normal or became demented.
"Of the 897 participants, there were 61 cases of dementia (6.8 percent) identified during the follow-up period, which, on average, was 3.3 years," says Dr. Holtzer.
"This figure is in line with what we'd expect for the incidence of dementia in this population," he adds.
Based on their observations, the researchers came to the conclusion that within-person variability across the tests predicted the development of dementia independently of how people performed on the tests.
They suggest that their findings be replicated in different populations before they are applied in a clinical setting.