Examining the role of the arcuate fasciculus on reading development by studying repetitive head impact

A myriad of changes occur as a child learns to read including in gray matter (e.g. word-selectivity in the visual word form area (VWFA)) and white matter (e.g. fractional anisotropy (FA) of the left arcuate fasciculus (AF)). Further, pre-readers at risk for developing dyslexia show lower FA in left AF, revealing potential white matter mechanisms that drive reading development. While we cannot know whether arcuate development is causally responsible for much of early reading ability without disrupting the system, here we explore this question by studying head impacts in otherwise typically-developing 8-12 year-olds. Youth football leagues usually start tackle football around age 8, when most children acquire literacy. We scanned eleven children before their initial season of tackle football and followed them longitudinally after the season, and compared their neurodevelopment to a matched control cohort. Preliminary findings show that at preseason, there are no significant between-group reading differences in VWFA selectivity, and FA in AF; however, we observed FA differences in the left AF postseason. Children who played their first season of tackle football showed no developmental changes in the left AF while control children showed increasing FA longitudinally (4-5 months). These white matter differences might precede observable deficits in reading, as we found no significant between-group differences in reading scores postseason (albeit trending, with modest reading score improvements in children in the control but not football group). Significant reading ability changes in typical development are expected at follow-up. Overall, these results suggest that exposure to repetitive head impacts may lead to atypical white matter development, and that the growth of the left AF may be especially important in driving reading development. Ongoing longitudinal investigations will explore whether children catch up in AF growth with increasing time post-season, and dose-response relationship of head impacts on reading and other cognitive outcomes.