Fig. 5.

Analysis of individual growth trajectories in the AF and ILF. a Left arcuate and ILF mean diffusivity (MD) time courses are correlated across individual subjects. For visualization, standardized MD values are plotted for each tract at each available time point for all subjects. Individual time courses are enlarged for a set of six example subjects to show greater detail. Individual AF and ILF time courses were positively correlated, and a cross-correlation analysis failed to detect a significant correlation at any non-zero lag, consistent with the interpretation that growth occurs in concert across tracts. b MD values were mean-centered for each subject, thus representing each subject’s time course of MD changes as modulations around their mean. Mean-centered values at each available time point are plotted for the AF vs. ILF showing tight correspondence between changes in these two tracts. c The time course of change in Reading Skill varies across subjects and is negatively related to individual white matter time courses: Within a subject, as MD decreases in the ILF, Reading Skill increase. For visualization, standardized Reading Skill and MD values are plotted for the ILF at each available time point for all subjects. As in a, time courses are enlarged for a set of six example subjects to show individual subject trajectories in greater detail. d Mean-centered MD values at each available time point for the ILF correlate with mean-centered Reading Skill assessed at each time point, demonstrating the relationship between time courses of MD and Reading Skill change. The scatter plots in b, d also make it clear that the time course of plasticity is more tightly coupled across tracts than it is to behavior. Hence, even though there is a statistically significant relationship between the time course of white matter and behavioral changes, there is also un-explained variance that is likely to be related to aspects of the intervention environment that do not directly impact behavior