Monday, August 22, 2016

Lifespan changes in brain and cognition - early life sets the stage.

Walhovd et al. present a fascinating study on the origins of lifespan changes in brain and cognition, defining an extensive cortical region wherein surface area relates positively to general cognitive ability (GCA) in development. They find evidence that especially prefrontal and medial and posterolateral temporal clusters relate more strongly to GCA:

Brain and cognition change with age, with early gains and later declines. Attempts have been made to identify age-specific mechanisms, focusing on when and how declines begin in adults. However, even though general cognitive ability declines with age, there is a high stability in individuals’ cognitive ability relative to their same-age peers. Here we show that the relation between brain and cognition appears remarkably stable through the human lifespan. The cortical area change trajectories of higher and lower cognitive ability groups were parallel through life. Birth weight and parental education were identified as predictors, which provides novel evidence for stability in brain–cognition relationships throughout life, and indicates that early life factors impact brain and cognition for the entire life course.
Neurodevelopmental origins of functional variation in older age are increasingly being acknowledged, but identification of how early factors impact human brain and cognition throughout life has remained challenging. Much focus has been on age-specific mechanisms affecting neural foundations of cognition and their change. In contrast to this approach, we tested whether cerebral correlates of general cognitive ability (GCA) in development could be extended to the rest of the lifespan, and whether early factors traceable to prenatal stages, such as birth weight and parental education, may exert continuous influences. We measured the area of the cerebral cortex in a longitudinal sample of 974 individuals aged 4–88 y (1,633 observations). An extensive cortical region was identified wherein area related positively to GCA in development. By tracking area of the cortical region identified in the child sample throughout the lifespan, we showed that the cortical change trajectories of higher and lower GCA groups were parallel through life, suggesting continued influences of early life factors. Birth weight and parental education obtained from the Norwegian Mother–Child Cohort study were identified as such early factors of possible life-long influence. Support for a genetic component was obtained in a separate twin sample (Vietnam Era Twin Study of Aging), but birth weight in the child sample had an effect on cortical area also when controlling for possible genetic differences in terms of parental height. Our results provide novel evidence for stability in brain–cognition relationships throughout life, and indicate that early life factors impact brain and cognition for the entire life course.
A summary graphic from the review by Jagust:

Conceptual model linking brain development, cognition, brain reserve, and late-life cognitive decline. Early life exposures and genes affect brain development, which in turn is related to GCA. GCA and education are related to one another, and provide brain reserve with advancing age. The graph demonstrates two individuals with high (blue) and low (red) brain reserve. Although the rate of their age-related cognitive decline is identical, the person with higher reserve crosses the threshold for dependence at an older age, thus experiencing a longer independent life. Early-life exposures, however, also confer indirect beneficial effects in addition to brain development, and these are likely to be salutary over the lifespan.

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