The neural correlates of skilled reading: An MRI investigation of phonological processing

Studies of reading development and disability have identified phonological skill as a major contributor to reading ability in children. The relationship seems to hold across a wide range of adult, skilled readers, as well, but its neural basis has yet to be identified. In order to examine the predictive power of phonological ability on adult reading ability, three studies were conducted in which both behavioral and neural indices of phonological processing were correlated with measures of oral reading fluency and silent reading comprehension. The first study investigated the influence of fMRI activity within the phonological processing network during a self-paced passage reading task. Regions of interest for phonological decoding were identified on an individual basis, using subjects' performance on a phonological lexical decision task. Activity during the natural passage-reading task in the left occipitotemporal region, posterior superior temporal gyrus, supplementary motor area, and anterior inferior frontal gyrus was positively correlated with reading measures, providing neural evidence for the relationship between phonological processing and adult reading ability. The second study aimed to identify interregion connectivity pathways that contribute to differences in reading ability. By comparing timecourses of activation within the individually localized regions of interest, it was discovered that superior readers showed more robust connections between two of the regions. Connection strength between posterior superior temporal gyrus and anterior inferior frontal gyrus was positively correlated with word recognition ability. In the third study, diffusion tensor imaging was performed on a larger sample of adult subjects to assess structural connectivity contributions to reading ability. Using a semi-automated tracing method, FA values of the corpus collosum and 7 bilateral tracts previously reported to be associated with reading ability were recorded. Positive correlations between reading ability and bilateral superior corona radiata, left inferior corticospinal tract, and right superior and inferior longitudinal fasciculus support previous hypotheses that higher integrity of white matter tracts connecting the reading network is one marker of superior reading ability. Altogether, the results indicate that highly skilled readers benefit from increased engagement of and stronger coherence within the phonological processing network during natural, everyday reading