Neural substrate in a case of foreign accent syndrome following basal ganglia hemorrhage

• We followed a case of foreign accent syndrome after left basal ganglia lesion for one year.
• We examined perceived speech, phonetic features, and functional changes of the brain.
• We found that lengthy speech therapy helped to improve abnormal segmental and prosodic symptoms.
• Functional MRI showed compensatory activations in the cortical and subcortical speech motor networks.
• We report that the basal ganglia is one of the important neural substrates for foreign accent syndrome.

Foreign accent syndrome (FAS) is a rare expressive language output disorder due to acquired inability to make the normal phonetic and phonemic contrasts of one's native dialect. A 37-year-old woman who was monolingual in Korean developed FAS after a left basal ganglia hemorrhage. We assessed perceived speech by phonetic analysis and diffusion tensor tractography (DTT) and performed functional magnetic resonance imaging (fMRI) using a picture naming task. One year after the onset of FAS, her initial English-like accent substantially improved to a Seoul accent, but was not completely recovered to the prestroke level. DTT showed disconnected and decreased numbers of fibers in the left arcuate fasciculus (AF), and these findings were unchanged when the patient was assessed at follow-up. The fMRI analysis showed activation on the bilateral cortical and subcortical speech-motor network: 1) the left cortical language area including Broca's area, the oromotor cortex, and the bilateral superior cerebellum, and 2) the right subcortical structures, including the caudate and thalamus. Our findings suggest that FAS may be caused by the disruption of the cortico-subcortical language network and that subcortical structures, including the basal ganglia, may have an important role in the development of speech motor control deficits in FAS. We also found that neuroplastic change in the damaged cortico-subcortical speech-motor network compensates for FAS and induces clinical improvement.