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
