THE NEURAL BASES OF READING FLUENCY: FROM STRUCTURE TO FUNCTION

Reading fluency is an often understudied aspect of reading, and it is uncertain if the neural correlates supporting fluency overlap with the traditional reading network or recruit out-of-network areas. Through a series of three studies that encompassed structural imaging, functional imaging, and direct manipulation through neuromodulation, the neural underpinnings of reading fluency were examined. The brain mechanisms supporting reading fluency may also overlap with those facilitating general cognitive processing speed, and therefore the behavioral and neural relationship between fluency and processing speed was also assessed. Results suggest that the ventral regions of the traditional reading network (i.e., occipitotemporal cortex, middle temporal gyrus) play a larger role in reading fluency as compared to dorsal regions, but that additional brain areas such as the precentral gyrus, superior parietal lobule, and insula also contribute to reading fluency, possibly by aiding attention. By modulating the right posterolateral cerebellum, we found evidence of this area supporting reading fluency ability in typical readers and reading accuracy in those diagnosed with developmental dyslexia but not processing speed for either reading ability level, suggesting that this region may play a more domain-specific role in reading rather than supporting general processing speed. Last, there was a lack of structural brain regions that correlated with both reading and processing speed scores. This suggests that the neural correlates of quick processing required for reading is reading-specific rather than associated with general processing speed ability that can be relied upon for broad cognitive tasks.