Older people don't become forgetful simply because of their age, they draw blanks because of diseases unfolding in their brains, a new study suggests. 

Even mildly forgetful seniors have brain lesions that cause memory lapses, yet they don't always progress to full-blown dementia, according to researcher Robert S. Wilson, a neuropsychologist at Rush University Medical Center in Chicago.

The new finding dispels the myth that memory impairment is just a normal part of aging, Wilson said. 

"On some level, we're arguing against the idea that normal cognitive aging is inevitable," Wilson told MyHealthNewsDaily. "It looks like even mild decline doesn't occur in people who haven't accumulated some of this pathology in the brain."

The brain changes related to forgetfulness are associated with aging, Wilson said, but aging alone does not cause the process.

New findings 
In the study, 350 Catholic nuns, priests and brothers were given annual memory tests for up to 13 years that included naming, number and reading assessments and a word list-recall test. After their deaths, the participants' brains were examined for lesions.

Lesions, such as abnormal protein plaques and tangled fibers, proliferate in the brains of people with Alzheimer's disease (AD), which affects more than 5 million Americans. Dementia, a condition marked by cognitive decline that interferes with daily life, is most often caused by AD.

The researchers found that almost none of those who had experienced gradual memory loss had brains free of lesions.

In the brains of people who had experienced gradual memory decline, the researchers found tangles and clumps of proteins. Wilson noted that for most, memory loss was gradual until the last four or five years of life.

People who had stokes or protein clumps called Lewy bodies in their brains also had nearly double the rate of gradual memory loss of those without these lesions.

Early changes go unnoticed 
"The take-home from this is that the pathologies traditionally associated with Alzheimer's and late-life dementias are strongly associated with early, mild changes in function," Wilson said. "It appears these brain lesions have a much greater impact on memory function in old age than we previously thought."

Future research needs to focus on determining why some people are more vulnerable to this disease process than others, and understanding how to slow its progression, Wilson said.

It appears that Alzheimer's begins to develop years or even decades before noticeable symptoms appear, he said, leading to the conclusion that those affected "spend a great deal of their old age successfully fighting off this disease."

"So much of the story of this disease is still untold," Wilson said.

The study was supported by the National Institute on Aging, and was published online Wednesday in the journal Neurology.

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