Math and reading skills greatly influence the socio-economic outlook of an individual. These skills have both shared (e.g. decoding of visual stimuli), as well as dissociated (e.g. quantity processing) cognitive components. Moreover, math and reading learning disabilities have a high-rate of co-occurrence, although some children have difficulties with only one skill or the other. Therefore, it is possible that math and reading have both shared and dissociated neural substrates, which are presently unknown. To address this significant gap in knowledge, we applied an innovative multi-modal approach, combining functional MRI (fMRI), diffusion MRI (dMRI), and quantitative MRI (qMRI), to identify and compare both the gray and white matter substrates of the math and reading networks. Through meticulous single-subject analyses, we showed that processing associated with math and reading occurs largely in parallel in the human brain. First, fMRI revealed that gray matter regions involved in processing math and reading are distinct, even though they neighbor in cortex. Second, dMRI showed that while the superior longitudinal (SLF) and the arcuate (AF) fascicles contribute to both math and reading networks, within these fascicles there are segregated and parallel sub-bundles of white matter tracts associated with math or reading. This organization is akin to parallel and distinct lanes in a highway. Third, qMRI measurements showed lower T1 relaxation time, which suggests a higher degree of myelination, in white matter tracts associated with reading than math. These novel findings: (i) open a new avenue of research enabling linkage of sub-bundles within fascicles to behavior and (ii) may explain both isolated and comorbid cases of math and reading disabilities, which may be associated with white matter abnormalities within sub-bundles or entire fascicles, respectively.
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