Neural organization of speech production: A lesion-based study of error patterns in connected speech

Brielle C Stark; Alexandra Basilakos; Gregory Hickok; Chris Rorden; Leonardo Bonilha; Julius Fridriksson

Specifically, verbal paraphasias during connected speech were significantly associated with damage to left hemisphere ventral stream areas whereas sound paraphasias during connected speech were associated with damage to left hemisphere dorsal stream areas. Neologisms were significantly associated with damage to left hemisphere dorsal stream regions, including the supramarginal gyrus, postcentral gyrus, precentral gyrus, posterior superior temporal gyrus and underlying white matter. When both lesion volume and apraxia of speech severity were regressed, the pattern of damage associated with neologisms was similar. Phonemic paraphasias, when regressing variance from only lesion volume, were significantly associated with damage to more left hemisphere dorsosuperior areas as compared to neologisms, centering on supramarginal gyrus, precentral gyrus and middle frontal gyrus (posterior segment) but subsequent regression of apraxia of speech severity alongside lesion volume did not result in significant clusters for phonemic paraphasias. This is likely the result of sampling, where the sample with apraxia of speech also tended to present with more anterior lesion damage. Semantically related paraphasias were most associated with damage to left hemisphere posterior superior and middle temporal gyri, extending anteriorly into superior and middle temporal gyrus, and also included damage to angular gyrus and underlying white matter (superior longitudinal fasciculus, inferior longitudinal fasciculus, and inferior fronto-occipital fasciculus). Finally, no significant clusters were found to be associated with unrelated paraphasias when regressing only lesion volume; however, with the additional regression of variance from apraxia of speech severity, unrelated paraphasias were significantly associated with more posterior damage compared with semantically related paraphasias. These regions included damage to left hemisphere posterior superior, middle and inferior temporal gyri, angular gyrus and underlying white matter (superior longitudinal fasciculus, inferior longitudinal fasciculus, and inferior fronto-occipital fasciculus).