Simply getting older is not the cause of mild memory lapses often called senior moments, according to a new study by researchers at the Rush Alzheimer's Disease Center. The study, published in the September 15, 2010, online issue of Neurology, the medical journal of the American Academy of Neurology, found that even the very early mild changes in memory that are much more common in old age than dementia are caused by the same brain lesions associated with Alzheimer's disease and other dementias.
"The very early mild cognitive changes once thought to be normal aging are really the first signs of progressive dementia, in particular Alzheimer's disease." said Robert S.Wilson, PhD, neuropsychologist at Rush University Medical Center. "The pathology in the brain related to Alzheimer's and other dementias has a much greater impact on memory function in old age than we previously recognized."
The study involved over 350 nuns, priests and brothers who participated in Rush's Religious Orders Study and completed up to 13 years of annual cognitive testing. After death, the brains were examined for the lesions associated with dementia: neurofibrillary tangles, cerebral infarction (stroke), and Lewy bodies.
Researchers looked at the rate of change in cognitive function over time. The last four to five years of life showed a very rapid decline. The preceding years showed a much more gradual decline that would be described as normal aging.
As expected, pathologic lesions were related to the rapid decline, but researchers were somewhat surprised to find the pathology was very strongly predictive of the mild changes in cognitive function.
Higher tangle density adversely affected all forms of cognition at all trajectory points. Both Lewy bodies and stroke approximately doubled the rate of gradual memory decline, and almost no gradual decline was seen in the absence of lesions.
"Our study finds that Alzheimer's disease and related dementias are the root cause of virtually all loss of cognition and memory in old age. They aren't the only contributing factors; other factors affect how vulnerable we are to the pathology and to its effects. But the pathology does appear to be the main force that is driving cognitive decline in old age," said Wilson.
According to Wilson, recognizing that the earliest changes in memory are related to Alzheimer's pathology can lead to early diagnosis and will be critical information if a treatment is developed that can alter the pathologic course of the disease.
The study was supported by the National Institute on Aging. Co-authors include Sue Leurgans, PhD; Patricia Boyle, PhD; Dr. Julie Schneider and Dr. David Bennett.
- Wilson et al. Cognitive activity and the cognitive morbidity of Alzheimer disease. Neurology, 2010; 75 (11): 990 DOI: 10.1212/WNL.0b013e3181f25b5e
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