(Ivanhoe Newswire) -- The belief that healthy older brains are substantially smaller than healthy younger brains may stem from studies that failed to screen out people whose undetected, slowly developing brain disease was killing off cells in key areas, according to new research. As a result, previous findings may have overestimated atrophy and underestimated normal size for the older brain.

The study tested participants in the Netherlands' long-term Maastricht Aging Study who were free of neurological problems such as dementia, Parkinson's disease or stroke. Participants took neuropsychological tests, including a screening test for dementia, at baseline and every three years afterward for nine years.

Participants were also given MRI scans at year three to measure seven different parts of the brain, including the memory-laden hippocampus, the areas around it, and the frontal and cingulate areas of the cognitively critical cortex.
 
After examining behavioral data collected from 1994 to 2005, the researchers divided participants into two groups. The first group had 35 cognitively healthy people who stayed free of dementia (average starting age 69.1 years); the second had 30 people who showed substantial cognitive decline but were still dementia-free (average starting age 69.2 years).

That cognitive decline was measured by declines of at least 30 percent on two or more of six core tests of verbal learning and fluency, recall, processing speed, and complex information processing, and/or decreases of 3 or more points (raising suspicion for cognitive impairment) on the Mini-Mental State Examination screening tool for dementia.

In contrast to the 35 people who stayed healthy, the 30 people who declined cognitively over nine years showed a significant effect for age in the hippocampus and parahippocampal areas, and in the frontal and cingulate cortices. In short, among the people whose cognition got worse, older participants had smaller brain areas than younger participants.

Thus, what had seemed to be age-related atrophy in gray matter more likely reflected pathological changes in the brain that underlie significant cognitive decline, rather than aging itself, the authors wrote. As long as people stay cognitively healthy, the researchers believe that the gray matter of areas supporting cognition might not shrink much at all.