Multimodal investigation of the speech planning network.
Zacà D., Sarubbo S., Dalla Bona M, Colarusso E., Pulcrano G., Rozzanigo U., Recla M., Chioffi F., Jovicich J.
Fluent speech production in humans is based on the skill of articulating sounds. A speech articulation network (SAN) has been observed in multiple studies using separate neuroimaging modalities. However several aspects of the SAN remain unknown including: a) the topography of this network at the whole brain level and b) the role of two main white matter bundles of the language dorsal stream, the arcuate fasciculus (AF) and the anterior portion of the superior longitudinal fasciculus (SLF III), in speech articulation. Furthermore the extraction of a SAN using independent component analysis has not been yet investigated. In this study we: i) computed the whole brain rs-fMRI intrinsic functional connectivity (iFC) of cortical sites that, stimulated intra-operatively at direct electrical stimulation, induced speech arrest; ii) reconstructed the SLF III and AF with tractography and analyzed the frequency and distribution of their cortical terminations in the functionally connected regions of the SAN; iii) compared the intra-operative SAN with the pre-surgery rs-fMRI ICA networks. The iFC maps of the SAN included frontal-parietal and temporal regions symmetrically distributed across the two hemispheres regardless of the side of speech arrest (left or right). In comparison with AF, the SLF III provided higher frequency and density of terminations in the cortical regions of SAN. ICA of pre-surgical rs-fMRI data showed promising results in predicting the SAN. The set of functional and structural information about the SAN obtained in this multimodal imaging study may guide future investigation of speech articulation disturbances.