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Late-life cognitive decline due to dementia and stroke may have its origins in childhood intelligence, according to a recent study. While previous studies have shown an association between educational level and late-life cognitive decline and dementia, researchers at the University of Edinburgh suggests that early childhood IQ might also be a predictor of late-life organic brain lesions associated with decreased cognitive function.

Studies were conducted on the 1936 Midlothian Cohort, a long-standing regional community of elderly people who had initially participated in the Scottish Mental Survey of 1947. This group is a unique cohort, as the subjects are age-matched (all born in 1936) and have childhood baseline intelligence data (all IQ-tested at 11 years of age.)

Brain lesions associated with stroke and dementia appear on MRI as white matter hyperintensities (WMHs). These are found in various locations, at various densities, sizes and contours in the white matter. While the etiology and functional-relationship of WMHs can be difficult to determine, their distinctive characteristics can be used to isolate lesions typical for specific insults: stroke, cerebrospinal fluid pressure abnormalities, and other cerebrovascular conditions. Improved image post-processing techniques now allow more discrete sorting of WMH variances, yielding cleaner correlations between lesion and inciting pathology or functional clinical presentation. In this case, Analyze software was used to differentiate stroke infarcts from other WMH occurrences.

The researchers demonstrated a significant association between WMHs and low age 11 IQ, which was stronger in subjects with evidence of stroke than in those with no stroke evidence, but independent of vascular risk factors. Incremental effects of WMH were associated with reduced cognitive ability and information processing speed, but not memory. Other correlates to increased WMH and cognitive processing were history of hypertension, older age, and female gender.

Researchers felt the results of this study were uniquely strengthened by the ability to control for variability by using the same community-dwelling population for childhood and elder years assessments; the methodological employ of both qualitative and quantitative WMH assessments, with exclusion of lesions per stage and state of cerebrovascular disease; and use of several cognitive tests, allowing for the exclusion of other variables potentially associated with cognitive decline.

They identified potential confounding factors such as use of WMH as the sole marker for cerebrovascular disease, self-reported medical histories, and prevalence of correlations between other variables (hypertension, age and gender) on cognitive processing and processing speed.

Nonetheless, a clear association between childhood IQ, increased WMH and lower late-life cognitive function was demonstrated, suggesting that early-life cognitive ability should be considered – along with proxies used in related research such as duration of education and educational attainment – as potential predictors of late-life cerebrovascular disease and cognitive function.

Tags: Brain Lesions, Dementia, IQ, Stroke