Neural correlates of foreign accent syndrome: Is white matter the key to the mystery?

Background: Foreign accent syndrome is a rare entity with neural underpinnings that are not yet fully understood. Cases of neurogenic foreign accent syndrome due to right hemisphere lesion are very uncommon. We investigated the cortical and white matter lesions in a patient to better understand this syndrome.

Case report: A 39-year-old French woman had a right middle cerebral artery stroke. This French native speaker was now perceived as speaking with an English accent, without signs of dysarthria or aphasia. Lesions involved right insula, pre-central gyrus and surrounding white matter tracts. After transformation in MNI-152 coordinate system, we compared the lesions in our patient with Tractotron software, a white matter tract tool providing a probability of fiber disconnection.

Discussion: Speech evaluation suggested a disruption in the speech output motor system. We found lesions within this system, in anterior frontal and insular cortices, in accordance with previous descriptions. Besides structural grey matter damage, white matter also exhibited damage related to the stroke, particularly the frontal aslant tract. Very few studies have focused on the specific role of this tract in speech motor programming, but a role in speech production and stuttering have been described. Some cases of foreign accent syndrome appeared consecutively to right hemisphere lesions. There is growing evidence suggesting that right hemisphere lesions might lead to subclinical alteration of prosody contributing to the emergence of foreign accent syndrome.

Conclusion: This study emphasizes the importance of analyzing subcortical areas and their associated tracts, which could play a crucial role in better understanding symptoms and anatomical correlation.