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Poster C48, Friday, August 17, 10:30 am – 12:15 pm, Room 2000AB

Reading efficiency is associated with fractional anisotropy, but not with myelin content, in the superior cerebellar peduncles.

Lisa Bruckert1, Katherine E. Travis1, Aviv A. Mezer2, Michal Ben-Shachar3, Heidi M. Feldman1;1Stanford University, 2The Hebrew University of Jerusalem, 3Bar Ilan University

Introduction: Microstructural properties of the cerebellar peduncles are positively and negatively associated with reading abilities in children and adolescents. In diffusion MRI (dMRI), white matter microstructure is typically indexed by fractional anisotropy (FA) - a measure of directionality of water diffusivity. FA can be influenced by multiple tissue properties, including myelin content, axonal diameter, and axonal density, making it difficult to interpret the direction of structure-function correlations and the tissue properties that underlie them. R1 from quantitative T1 (qT1) imaging is directly associated with myelin content (R1 = 1/T1). Integrating measures of FA and R1 allows us to examine the unique and overlapping contributions of these white matter metrics on individual variation in reading efficiency. If both measures correlate comparably with reading, the results would suggest that these associations are driven by myelin content. In contrast, associations of FA with reading in the absence of correlations with R1 would suggest that these associations are driven by axonal tissue properties. Methods: 23 children were assessed at age 8y with standardized tests of reading accuracy and fluency, as measured by the Test of Word Reading Efficiency, 2nd edition (TOWRE-2, Torgesen, Wagner & Rashotte, 1999). Each child underwent dMRI and qT1 imaging at 3T. In dMRI, we applied a dual-spin echo diffusion-weighted sequence (30 directions, b=1000 s/mm2, 3 b=0 volumes). In qT1, we applied a spoiled gradient echo sequence, using a number of different flip angles and inversion times. We used Automated Fiber Quantification (Yeatman et al., 2012) to segment and extract the mean tract-FA (based on dMRI) and mean tract-R1 (based on qT1) of the superior (SCP), middle (MCP), and inferior cerebellar peduncles (ICP) in each child. Pearson correlations were calculated to examine the associations between word reading scores and tract-FA or tract-R1. Results: Tract-FA of the left SCP negatively correlates with word reading (rP(21)=-.43, p=.040). In the right SCP, we observe a correlation of similar strength that approaches significance (rP(21)=-.37, p=.079). While tract-FA is strongly correlated with tract-R1 in these peduncles (left SCP: rP(21)=.63, p<.001; right SCP: rP(21)=.76, p<.001), tract-R1 of the left and right SCP does not correlate with word reading (p>0.2). Moreover, within the right SCP, the correlation between tract-FA and word reading becomes significant when we control for tract-R1 (rP(20)=-.46, p=.031). Associations between white matter metrics of the other cerebellar peduncles and word reading are not significant. Discussion: Our findings replicate, in an independent sample of 8y old children, the negative association between FA of the left SCP and reading proficiency, previously recorded in older children and adolescents (Travis et al., 2015). The lack of association between reading and R1 suggest that correlations of FA and reading are driven by axonal properties. The combination of these techniques helps to explain negative associations of FA and reading in the SCP and implicates axonal diameter or number of crossing fibers as the critical tissue properties for reading efficiency. Determining which of these factors is relevant requires additional MRI technologies and analyses.

Topic Area: Language Development