Neural substrates of the 'low-level' system for speech articulation: Evidence from primary opercular syndrome.

We describe a patient with progressive disorder of speech, without language impairment (opercular syndrome). Morphometric analysis confirmed asymmetric volume reduction of the precentral areas (>left). Diffusion imaging showed significant white matter changes in the left frontal lobe, with specific involvement of the left corticobulbar tract and connections between supplementary/pre-supplementary motor areas and the frontal operculum (frontal aslant tract). We suggest that the organization of expressive language includes a 'low level' motor system principally distributed in the left hemisphere that shows specific susceptibility to neurodegeneration, distinct from neural systems subtending praxic, and cognitive aspects of language.