St. Paul, Minn. – Determining what a person’s level of mental functioning was prior to the onset of dementia, and thereby the degree of cognitive decline, is important to both clinicians who treat people with dementia and to researchers. Until now, there has been a limited array of data available or considered valid in estimating an individual’s level of pre-dementia cognitive functioning.
According to a study reported by McGurn et al in the April 13 issue of Neurology, the scientific journal of the American Academy of Neurology, researchers from the University of Edinburgh, UK, have shown that it is possible to use a straightforward reading test to estimate validly how well persons functioned before they were affected by dementia.
The diagnosis of dementia depends on demonstrating cognitive decline from a prior level, ideally by comparing current status with observed pre-onset cognitive function. However, it is rare to have available an assessment of pre-dementia cognitive function, and so clinicians and researchers have used estimates. One such estimate is provided by the National Adult Reading Test (NART), a British test devised by Hazel Nelson in the 1980s.
The NART requires people to try to pronounce words that do not follow the usual rules of pronunciation. People who get more of these correct tend to have had higher mental functioning. Importantly, this sort of ability does not decline much with age and is thought to hold quite well, compared with other mental skills, in the early stages of dementia. Until now, though, no one had compared the NART scores of demented people and non-demented people with their cognitive function from youth.
“Our study posed two questions concerning the NART,” notes Ian Deary, PhD, Department of Psychology. “First, does mild to moderate dementia reduce NART scores? And second, do both non-demented and demented subjects show the same association between mental ability in youth and NART scores in old age?”
Deary and his team of researchers compared recent NART scores of 509 people with IQ scores from their youth. These 509 subjects had participated in the 1932 Scottish Mental Survey at age 11. This landmark survey of 87,498 children born in 1921 measured psychometric intelligence using a version of the Moray House Test Number 12, a 45-minute IQ-type test.
The researchers differentiated the 509 subjects into two groups: one group of 45 who developed dementia in old age and another group of 464 who did not. Those with dementia scored lower on NART and had lower childhood mental ability scores. After statistically controlling for childhood mental ability, there was no difference in NART scores between the demented and non-demented groups, and the correlation between NART scores and childhood ability test scores was very similar in the two groups. “Our findings indicate that the National Adult Reading Test is a valid estimator of pre-onset cognitive ability in persons with mild to perhaps moderate dementia,” says Deary.
“The NART, at least in this sample, has passed a robust assessment of its validity as an estimator of pre-dementia cognitive ability,” concludes Deary. “Our results show a constant relationship between NART and childhood ability in the context of very different levels of current cognitive status.” Where there is greater childhood mental ability, the aspects of memory involved in pronunciation of irregular words remain relatively intact. “Among the declining cognitive skills of a person’s brain in early dementia, the ability to perform the NART stands out as a relatively resistant indicator of how good this brain used to be.” Deary and his team note, however, that for subjects with a more severe degree of dementia, the relationship between NART scores and early childhood ability would probably not remain as steady.
This study was supported by funding from the Alzheimer’s Research Trust and the Biotechnology and Biological Sciences Research Council (UK).
The American Academy of Neurology, an association of more than 19,000 neurologists and neuroscience professionals, is dedicated to improving patient care through education and research. A neurologist is a doctor with specialized training in diagnosing, treating and managing disorders of the brain and nervous system such as stroke, Alzheimer's disease, epilepsy, Parkinson's disease, autism and multiple sclerosis.
For more information about the American Academy of Neurology, visit www.aan.com.
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Editor's Notes: An editorial by Douglas K. Detterman, PhD, commenting on this study is also published in the April 13 issue of Neurology.