Corpus callosum microstructure and auditory interhemispheric transfer in spina bifida myelomeningocele
Bradley, Kailyn A. L.
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The purpose of this study was to evaluate if early disruption in corpus callosum development due to spina bifida myelomeningocele (SBM) contributes to plastic reorganization of interhemispheric white matter. Additionally, this study evaluated if diffusion tensor imaging measures of integrity of the interhemispheric temporal tract specifically had functional relevance and predicted performance on a task that required auditory communication between hemispheres, dichotic listening. T1-weighted and diffusion tensor imaging data was acquired on a group of people with SBM (n = 76) and a typically developing group (n = 27). Probabilistic tractography was performed to isolate the interhemispheric white matter connecting auditory processing regions in both hemispheres. Behavioral performance was assessed on a consonant-vowel dichotic listening task in a subset of these participants (SBM, n = 45; TD, n = 15). The key finding from this study was that atypical development of the corpus callosum in SBM does result in re-routing of interhemispheric temporal connections through alternate commissures, particularly the anterior commissure. These re-routed fibers were present in people with SBM and a hypoplastic, or thin posterior corpus callosum, as well as those with more severe underdevelopment, partial agenesis. Additionally, microstructural integrity was reduced in the interhemispheric temporal tract in SBM, as indicated by lower fractional anisotropy and axial diffusivity, and higher radial diffusivity. Examination of macrostructure and microstructure of the tract and dichotic performance suggests that these re-routed connections through the anterior commissure are not compensatory, but maladaptive. Preservation of the normative pattern on the dichotic listening task in people with SBM is the result of connections between temporal lobes through the posterior corpus callosum, and not the anterior commissure. Lastly, abnormal AD was associated with atypical left ear performance on the dichotic listening task, suggesting that reduced integrity of the auditory interhemispheric tract adversely affected dichotic performance in SBM. Given persistent hypotheses about the role of the anterior commissure and other potential compensatory connections, this study has important implications for understanding of the effects of early corpus callosum maldevelopment, especially when partial agenesis is involved.