What's the science?

Reading ability has been linked to properties of white matter tracts; the myelinated (i.e. insulated) bundles of nerve fibers that connect various brain regions. Variation in the integrity of white matter is associated with certain aspects of reading ability. White matter plasticity including myelination in response to brain activity can occur on short time scales (days to weeks) and evidence suggests that it may promote learning. This week in Nature Neuroscience, Huber and colleagues test whether white matter plasticity occurs during a longitudinal reading intervention in children who are struggling readers.

How did they do it?

Grade-school aged youth were recruited and underwent intensive reading training for 4 hours a day, 5 days a week for 8 weeks. The participants were tested for reading skills and scanned using diffusion MRI (which measures white matter) prior to the reading intervention and throughout the intervention at 2.5 weeks, 5 weeks and 8 weeks (the end of intervention). A control group who did not receive the intervention was also tested and scanned. Individual differences in reading skill were measured using a composite score from a battery of reading tests. White matter structural properties were measured using diffusion tensor imaging in 3 major white matter tracts of the brain (the arcuate fasciculus, inferior longitudinal fasciculus and the corpus callosum) and reading skill was tracked over time in the reading intervention group and controls.

What did they find?

Prior to reading intervention, reading skill level was correlated with fractional anisotropy, which is a measure of the directionality of water diffusion within brain tissue. This measure is informative because water diffusion is more directional when tracts are organized coherently, as opposed to dispersed, and also when tracts are highly myelinated (i.e., well insulated). A significant improvement in reading skills and white matter tract changes were seen in response to the reading intervention. White matter structure changed: mean diffusivity (a measure that decreases with tissue density) was reduced over time while fractional anisotropy was increased over time in two major white matter tracts (the arcuate fasciculus and the inferior longitudinal fasciculus). Plasticity was also observed in a large collection of tracts extending beyond those conventionally associated with reading skills. These results suggest that reading intervention induces plasticity in white matter in general, which is related to improvements in reading skills in struggling readers. Lastly, they tested whether changes in the different white matter tracts occurred simultaneously along with improvement in reading skill and found that these changes were highly correlated over the intervention period, suggesting that the learning is happening along with changes in white matter tract structure.