The role of the Inferior Longitudinal Fasciculus in language production: evidence from bimodal and unimodal bilinguals.

The present study investigates the effect of language modality in the Inferior Longitudinal Fasciculus (ILF), an indirect pathway of the ventral language network, which seems to play an important role in visual object recognition and in lexical access, but which still need further investigation. A group of bimodal bilinguals and a group of unimodal bilinguals have been compared using Diffusion Imaging Tractography based on the Spherical Deconvolution approach. Behavioral measures of language production (picture naming and fluency tasks), and comprehension (detection of semantic, syntactic or lexical violations) have also been collected in both L1 (Italian) and L2 (English or Italian Sign Language, LIS). Results show that a faster lexical access in picture naming is associated with more number of tracts and volume in the ILF for oral languages but not for sign language, that is, in Italian (L1) and English (L2), but not in LIS (L2). No associations were observed between the ILF and any of the comprehension tasks. These results suggest a critical role of the ILF in lexical access during picture naming, specific for oral language modality.