Early left-hemispheric brain lesions: When is Language Comprehension Reorganized?

Aims: Early lesions of the left hemisphere (LH) induce reorganization of the productive language network to the right hemisphere, if a) anterior language cortex or b) the facial motor tracts are damaged. One of the first steps in the acquisition of speech and language production is the production of speech sounds, where the facial motor tracts play a crucial role. It is still unclear, however, which structures are relevant for LH processing of language comprehension in children with congenital LH brain lesions. We conducted a lesion-symptom-mapping study to identify brain structures possibly triggering the reorganisation of language comprehension if damaged early in brain development.

Methods: 11 Patients with congenital lesions of the LH (3 cortico-subcortical, 8 periventricular lesions) performed a language comprehension task during fMRI. BOLD signals were assessed with respect to lateralization and classified as typical (bilateral or left hemispheric) or atypical (right hemispheric) language representation. T1-weighted high-resolution 3D datasets were used to generate individual lesion masks, allowing to compare lesions of patients with typical representation to those of patients with atypical representation.

Results: A subtraction analysis for lesion sites of patients with atypical vs. typical representation of language comprehension revealed a region in the peri-insular white matter being lesioned in most patients with but not in patients without language reorganization. The critical region can be attributed to left arcuate fascicle.

Conclusion: It is well established that the left arcuate fascicle plays an important role in the phonological analysis of language input, and there is evidence for a very early lateralization of this function to the LH. As phonological analysis of speech input is crucial for the very early phases of language acquisition in infants, it is conceivable that damage to the arcuate fascicle might induce reorganization of language comprehension.

early brain lesions - language - reorganization