Abstract
While researchers have gained a richer understanding of the neural correlates of executive function in adulthood, much less is known about how these abilities are represented in the developing brain and what structural brain networks underlie them. Thus, the current study examined how individual differences in executive function, as measured by the Trail Making Test (TMT), relate to structural covariance in the pediatric brain. The sample included 146 unrelated, typically developing youth (80 females), ages 9–14 years, who completed a structural MRI scan of the brain and the Halstead-Reitan TMT (intermediate form). TMT scores used to index executive function included those that evaluated set-shifting ability: Trails B time (number-letter sequencing) and the difference in time between Trails B and A (number sequencing only). Anatomical coupling was measured by examining correlations between mean cortical thickness (MCT) across the entire cortical ribbon and individual vertex thickness measured at ~81,000 vertices. To examine how TMT scores related to anatomical coupling strength, linear regression was utilized and the interaction between age-normed TMT scores and both age and sex-normed MCT was used to predict vertex thickness. Results revealed that stronger Trails B scores were associated with greater anatomical coupling between a large swath of prefrontal cortex and the rest of cortex. For the difference between Trails B and A, a network of regions in the frontal, temporal, and parietal lobes was found to be more tightly coupled with the rest of cortex in stronger performers. This study is the first to highlight the importance of structural covariance in in the prediction of individual differences in executive function skills in youth. Thus, it adds to the growing literature on the neural correlates of childhood executive functions and identifies neuroanatomic coupling as a biological substrate that may contribute to executive function and dysfunction in childhood.
Highlights
For over 150 years, scientists studying cognition have noted the important role of the frontal lobes in the regulation of behavior and cognition
Our primary research question was as follows: Is stronger Trail Making Test (TMT) performance in childhood associated with greater cross-cortical covariance in regions of cortex thought to be relevant to executive functions? Stated another way, is the thickness of the prefrontal cortex and other cortical regions more highly correlated with the thickness of the rest of cortex in those with higher TMT scores?
Because the focus of the manuscript was on regions of the cortex in which mean cortical thickness (MCT) and vertex thickness correlations varied as a function of TMT performance, we have elected to leave the findings for main effects of MCT and TMT performance out of Figure 1
Summary
For over 150 years, scientists studying cognition have noted the important role of the frontal lobes in the regulation of behavior and cognition (see Braver and Ruge, 2006 for a review). While early investigations focused mainly on adult clinical populations, more recent research has described the protracted development of both executive functions and the frontal lobes within the context of normative development. Studies of the protracted nature of the development of executive functions within the context of typical development span several decades. Starting with the early work of Welsh and Pennington (1988) and continuing to more recent investigations (Hooper et al, 2004; Luciana et al, 2005; Huizinga et al, 2006; Conklin et al, 2007), a large corpus of data exists documenting that youth continue to make gains in performance on several different executive function tasks into the mid to late teens (Luna et al, 2004; Luciana et al, 2005)
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