Abstracts

Rationale: The non-dominant, typically right, hemisphere may take over language function after focal injury of the dominant hemisphere in early life. Yet, it still remains unknown which specific neural pathways are structurally reorganized in the non-dominant hemisphere to compensate for post-operative language decline. The present study investigated whether the disruption of pre-existing language pathway in the dominant hemisphere may induce structural reorganization in the non-language dominant hemisphere in patients who underwent epilepsy surgery. Methods: The study cohort included nine children with left-hemispheric seizure focus and left-hemispheric language dominance confirmed by functional MRI and intracranial stimulation mapping (age: 10.33.0 years old; 2 boys; 5/3/1 temporal/frontal/parietal resection; 7 seizure free). Pre-/post-operative Diffusion Tensor Imaging (DTI) data were acquired using a 3-tesla MRI at 55 encoding gradient directions with b-value=1000 sec/mm2. Pre-/post- DTI were performed, on average, 3.2 months prior to and 9.5 months after surgery. All children had neurocognitive assessments including CELF4 language assessment within a month of DTI acquisitions. In the right hemisphere of pre-/post-operative DTI, a total of 54 cortical regions of interest (ROI) was parcellated for DTI-connectome analysis. At each ROI, betweeness centrality measuring the number of neighboring axonal paths that pass through the ROI was calculated to evaluate the association between post-operative increase of this DTI parameter and language improvement. Results: Three of the 9 children had post-operative improvement in their expressive language. Parametric Pearson correlation analysis showed that post-operative change in Expression Language Index (ELI) score was positively correlated with post-operative change in betweeness centrality measured at the right paracentral lobule (Fig. 1, R2=0.48, p-value=0.03). Of note is a very large post-operative increase in betweeness centrality in three children with post-operative expressive language improvement. Interestingly, the subsequent analysis to identify all inter-regional connections to the parecentral lobule within 2 path lengths revealed that only these three children had post-operatively increased cerebellar ROIs connected to the paracetral lobule via the thalamic pathway (Fig. 2) Conclusions: Although preliminary, the present study suggests that the right hemispheric paracentral lobule-cerebellar connection may be strengthened to compensate for language decline in children who underwent left hemispheric resection. Further studies in larger samples with various resection locations are warranted to determine whether this pathway positively contributes to compensate for other functional reorganization, especially sensory and motor function. Funding: This study was funded by a grant from National Institute of Neurological Disorders and Stroke (R01-NS089659 to J.J).