Scientists in the US discovered that elderly people who had no mental decline had larger brains than Alzheimer's patients, even though their brain tissue showed signs normally associated with the disease.

The discovery is being presented this week at the American Academy of Neurology meeting in Chicago, by researchers from the Oregon Health and Science University (OHSU) in Portland.

The researchers working at the OHSU Layton Aging & Alzheimer's Disease Center discovered that brain volume and the occurrence of mental decline are linked in people with Alzheimer's.

Autopsy examinations of elderly deceased patients showed that the volume of the whole brain, and particularly the hippocampus (a region that sits at the base of the brain and is thought to be involved with encoding long term memory and emotions) tended to be larger in those patients who had not suffered cognitive impairment when they lived.

But the brains of these "healthy" patients still had the characteristic large clusters of protein plaques and tangles normally associated with Alzheimer's.

As co-investigator Dr Deniz Erten-Lyons, an assistant professor of neurology in the OHSU School of Medicine and a staff neurologist at the Portland Veterans Affairs Medical Center explained:

"Prior to death, these people did not suffer from mental decline. We also noted that these healthy study subjects had brain volumes that were on average, larger than the brain volumes of the Alzheimer's subjects we studied."

The researchers examined the brains of 36 deceased patients, comprising 12 people who did not have symptoms of Alzheimer's before they died (no cognitive impairment) and 24 who did.

Using MRI (magnetic resonance imaging), they found the brains of the "healthy" subjects were about 10 per cent larger by volume than those of the Alzheimer's patients.

Senior scientist on the study, Dr Jeffrey Kaye, who is director of the Layton Aging and Alzheimer's Disease Center and a professor of neurology in the OHSU School of Medicine said:

"We are hopeful that this research will help us further understand the structural and genetic ties to Alzheimer's disease and perhaps offer clues that may help us develop new drugs or therapies."

"We should caution that at this point we do not believe brain volume is an accurate tool for diagnosing the disease. However, in the future, this correlation could be helpful to doctors and researchers alike," he added.

Although the study is quite small, it was well received in some quarters.

Professor Clive Ballard from the Alzheimer's Society in the UK, told the BBC the discovery "exciting" and needed "more exploration".

Ballard said it was consistent with other studies that showed "people with higher levels of education or cognitive reserve may be protected from some of the effects of dementia".

Source: OHSU press statement, BBC News.

Written by: Catharine Paddock, PhD