Lateralization of language pathways in children as assessed using fMRI-guided probabilistic tractography

Aims: It is well-known that language is not processed symmetrically, with a left-dominant pattern in most subjects. Previous studies in adults showed a stronger structural connectivity between inferior-frontal and superior-temporal language regions (traditionally known as Broca's and Wernicke's region) on the left as compared to the right hemisphere. Using template based MR tractography Catai (Catani, PNAS2007) could show, that especially the arcuate-fasciculus is strongly lateralized towards the left hemisphere. However, this approach is difficult to apply in children as it relies on the generation of accurate cortical seed/target masks. For the developing brain, simple anatomical masks are not suitable (Brauer2011).

Methods: Overall, data from 16 healthy children could be included (age 11±3y, 8f). Children were scanned on a 1.5T Avanto scanner. We used two previously established fMRI paradigms to localize Broca's and Wenrnicke's territory on the dominant hemisphere for each subject individually. The locations were mirrored from the dominant onto the contralateral hemisphere. Around these four locations, spherical ROI's were places and used pairwise as seed and target for spherical deconvolution probabilistic tractography. Tractography was initiated in Wernicke's territory and tracks were selected and kept if they passed through a large inferior-parietal ROI around the central part of the arcuate fasciculus and passed in Broca's territory. The number of tracks connecting the two brain areas on the left and right side were counted. These numbers were compared against anatomical driven tractography, using a Mann-Whitney Test and assuming significance at p<0.05.

Results: fMRI-driven tractography shows a statistically significant lateralization of the arcuate fasciculus towards the left side p<0.01. Simple anatomical-mask-based tractography yields lateralization only at trend-level p>0.05.

Conclusion: Structural lateralization of the language pathway already exists in children. DTI combined with fMRI may prove to be a useful tool to asses hemisperic specialization for language reliably even in this age group.

lateralization of the language pathway - DTI - tracktografie - fMRI