Forgetting someone's name, losing track of a parked car or misplacing a set of keys may be common occurrences in adulthood, but there is nothing normal about them, a new study claims.
Even mild mental decline is connected to brain lesions associated with Alzheimer's disease and other forms of dementia, the study found.
Abnormal proteins called Lewy bodies and neurofibrillary tangles - both indicators of Alzheimer's disease - and evidence of strokes were present in the brains of all participants in the study who showed even mild to moderate mental decline.
Without such lesions, no decline in mental acuity occurred, according to the 16-year study of 354 Catholic nuns, priests and brothers. The lesions, or lack of them, were found during autopsies.
Study author Robert S. Wilson, senior neuropsychologist at the Rush Alzheimer's Disease Center at Rush University Medical Centre, said little is known about the causes of mental decline in aging adults.
"We know that when people get older they lose cognition, but it doesn't happen to everybody," said Wilson. "One way of thinking about these declines is that perhaps the neurofibrillary tangles and Lewy bodies found in the brain are part of a dynamic function that only impairs function when it damages a neuron."
Lifestyle factors can protect otherwise vulnerable people from mental decline, said Wilson, who is also a neurology professor at the medical school. These include having an active social life, intellectual pursuits, and moderate alcohol consumption. Research has also shown that higher levels of education protect against dementia, he added.
The ongoing research, begun in 1994, assessed verbal fluency, perceptual speed, IQ and episodic, semantic and working memory up to 14 times before study participants died.
Semantic memory is stored information; working memory is the ability to hold information at one time in order to learn. Episodic memory allows recollection of personal history. Separate scores were made for each measure.
No decline in global cognition, a composite of the separate scores, was found in people with low levels of tangles and Lewy bodies, according to the study published in the journal Neurology.
Among those whose data has been analysed, 47.5% had dementia when they died, and most of their decline occurred in the last four to five years of life. The findings were consistent with other research, according to the study.
The good news, said D. John Hart, a professor of behavioral and brain sciences at the University of Texas, Dallas, is that common memory lapses and mild to moderate decline in mental acuity does not predict Alzheimer's. Nor were they correlated with dementia at the end of life in the study.
"I wouldn't view this [study] as a cautionary tale or worry about these findings," said Hart, also a professor of neurology and psychiatry at the university. "This is more of a positive finding in that it offers the hope that people won't have to go through the cognitive declines that we just attribute to age."
New therapies can be targeted at the underlying pathologies, he said, noting that a large amount of research is under way in this area.
"I think we're getting to a place where what we used to assume was a normal 'fait accompli' doesn't have to happen," said Hart, adding that there can be other reasons for momentary mental lapses.
"Just because someone has blips or a momentary lapse of some kind, or something doesn't always work perfectly, doesn't mean there are those kinds of problems [Lewy bodies, tangles or strokes]," he said. "When you see a regular pattern, or something is affecting your life, that's when you might have an issue, and want to get checked out."
Same advice as before
In light of the findings, the same medical advice of the past applies, said Hart: "Keep an eye on diabetes and high blood pressure, quit smoking."
Hart said that certain types of mental functions are often well-preserved and "a great resource" at the end of life, such as semantic memory and the knowledge that comes from experience.
While the study found a strong connection between lesions and mental decline, not all participants had the same levels of Lewy bodies and tangles in their brains. This finding suggests that other unknown factors are involved in steep loss of mental functions in the years just before death, the researchers noted.
The study authors note that their research has certain limitations, such as the select group of participants. They conclude that the findings' general applicability "remains to be determined."
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