Duke University Medical Center researchers used functional magnetic resonance imaging technology to identify the marker.

The study focused on people with mild cognitive impairment, or MCI -- a condition that affects approximately 4 million to 5 million people in the United States. About 30 percent to 50 percent of MCI subjects develop Alzheimer's disease within five years of diagnosis.

Duke researchers used fMRI on people with MCI to track regions of the brain that become active or inactive when participating in tasks that involve memory. They then followed the subjects to document progression to Alzheimer's.

"A single baseline fMRI measure of deactivation could help predict which individuals will convert to Alzheimer's over the next several years," said the study's lead author, Dr. Jeffrey Petrella. "On the other hand, the fMRI scans of MCI subjects who did not convert looked more like those of healthy normal people, and could therefore be reassuring."

The research is detailed in the online journal PLoS One.