The method by the scientists at Cornell University also allowed research to accurately predict who is more likely to develop cognitive impairment without expensive tests or invasive procedures.
Charles Brainerd, professor of human development and the study's lead co-author with Valerie Reyna, director of the Institute for Human Neuroscience and professor of human development, both in Cornell's College of Human Ecology said that the memory abilities affected by cognitive impairment differ from those affected by healthy aging, resulting in unique error patterns on neuropsychological tests of memory.
Their theory-driven mathematical model detects these patterns by analyzing performance on such tests and measuring the separate memory processes used.
"With 10 or 15 minute recall tests already in common use worldwide, we can distinguish individuals who have or are at risk for developing cognitive impairment from healthy adults, and we can do so with better accuracy than any existing tools," Brainerd said.
The researchers said that the notion that memory declines continuously throughout adulthood appeared to be incorrect.
To develop their models, the team used data from two longitudinal studies of older adults and found that declines in reconstructive memory were associated with mild cognitive impairment and Alzheimer's dementia, but not with healthy aging.
Declines in recollective memory - recalling a word or event exactly - were a feature of normal aging.
Over a period of between one and a half to six years, declines in reconstructive memory processes were reliable predictors of future progression from healthy aging to mild cognitive impairment and Alzheimer's dementia, and better predictors than the best genetic marker of such diseases.
Reyna said that reconstructive memory is very stable in healthy individuals, so declines in this type of memory are a hallmark of neurocognitive impairment.
The study is published in the Journal of Experimental Psychology: Learning, Memory and Cognition.