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

Neologistic and phonemic paraphasias during connected speech associated with damage to left frontoparietal cortex. Neural models of motor speech control suggest that the left postcentral and supramarginal gyri are core areas for the mapping of somato-phoneme targets prior to production (Guenther . CC-BY-NC-ND 4.0 International license is made available under a The copyright holder for this preprint (which was not peer-reviewed) is the author/funder. It . https://doi.org/10.1101/544841 doi: bioRxiv preprint and Vladusich, 2012; Hickok, 2012). As neologistic errors likely arise from phonological selection and/or substitutions, this result supports the supposition of the role of the dorsal stream in phonological retrieval (Hickok and Poeppel, 2007; Schwartz et al., 2012) . In general, few studies have evaluated brain damage associated with phonemic paraphasias in aphasia comparative to verbal paraphasias, and they have differed in their conclusions as to the loading of phonemic paraphasias onto the left hemisphere dorsal or the ventral stream of language (Kreisler et al., 2000; Schwartz et al., 2012) . We found phonemic paraphasias during connected speech to be associated with frontoparietal left hemisphere brain damage. Notably, this result was only significant after removing variance from lesion volume but not apraxia of speech severity, suggesting a role for both word selection and motor planning in phonemic paraphasias produced during connected speech. Of particular interest is the robustness of VLSM results for sound paraphasias (neologistic, phonemic) derived during connected speech. In the present study, analyses performed on sound paraphasias from the connected speech task, and not the naming task, demonstrated significant results following removal of lesion volume variance and related apraxia of speech variance. Therefore, connected speech may be a particularly sensitive task on which to further evaluate lexical-phonological processing in the brain.