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Prosodic production tasks during fMRI reveal functional deficits in stutterers

Christian Kell, Katrin Neumann, Anne-Lise Giraud

Persistent developmental stuttering can be interpreted as the result of impaired linguistic motor executive function. Previous studies revealed pathologies in somatomotor as well as language-related cortices of stutterers. Frontal opercular regions (Broca and its right-hemispheric homologue) appear differentially activated in stutterers when compared with healthy controls. Stutterers seem to compensate their defect spontaneously via an activation of the right frontal operculum, while after fluency-shaping therapy a more left-lateralized frontal activation can be observed. Based on these findings, we sought to preferentially activate either the left or the right frontal lobe. Prosody perception usually involves lateralized cortical networks depending on whether it emphasises linguistic or emotional features. We therefore hypothesized that a similar functional lateralization should be observed in frontal regions during speech production emphasizing different prosodic features. While production of linguistic prosody should predominantly activate left-hemispheric regions, emotional prosody should reveal a more right-hemispheric network. The production of linguistic prosody should therefore reveal in a very selective manner relative left-hemispheric deactivations in stutterers, while production of emotional prosody should tell us more about the functional meaning of right frontal overactivations in stutterers relative to controls. After confirming functional lateralization of spoken prosody in normal subjects we compared activations in stutterers and controls. Despite similar behavioural performances, we found a very circumscribed left frontal deactivation in stutterers in the linguistic prosodic task in Broca’s area. The emotional prosodic task activated larger fronto-temporal networks in stutterers, but no significant differences were found in the group analysis. Our results delineate a focal functional lesion in the stutterers’ left language executive network, which may require compensation by Broca’s right homologue.


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