ALTERED PATTERNS OF CEREBRAL-ACTIVITY DURING SPEECH AND LANGUAGE PRODUCTION IN DEVELOPMENTAL STUTTERING - AN H-2 O-15 POSITRON EMISSION TOMOGRAPHY STUDY

To assess dynamic brain function in adults who had stuttered since chi ldhood, regional cerebral blood flow (rCBF) was measured with H2O and PET during a series of speech and language tasks designed to evoke or attenuate stuttering. Speech samples were acquired simultaneously and quantitatively compared with the PET images. Both hierarchical task co ntrasts and correlational analyses (rCBF versus weighted measures of d ysfluency) were performed. rCBF patterns in stuttering subjects differ ed markedly during the formulation and expression of language, failing to demonstrate left hemispheric lateralization typically observed in controls; instead regional responses were either absent, bilateral or lateralized to the right hemisphere. Significant differences were dete cted between groups when all subjects were fluent-during both language formulation and nonlinguistic oral motor tasks-demonstrating that cer ebral function may be fundamentally different in persons who stutter; even in the absence of stuttering. Comparison of scans acquired during fluency versus dysfluency-evoking tasks suggested that during the pro duction of stuttered speech, anterior forebrain regions-which play an a role in the regulation of motor function-are disproportionately acti ve in stuttering subjects, while post-rolandic regions-which play a ro le in perception and decoding of sensory information-are relatively si lent. Comparison of scans aqcuired during these conditions in control subjects, which provide information about the sensorimotor or cognitiv e features of the language tasks themselves, suggest a mechanism by wh ich fluency-evoking manoeuvers might differentially affect activity in these anterior and posterior brain regions and may thus facilitate fl uent speech production in individuals who stutter Both correlational a nd contrast analyses suggest that right and left hemispheres play dist inct and opposing roles in the generation of stuttering symptoms: acti vation of left hemispheric regions appears to be related to the produc tion of stuttered speech, while activation of right hemispheric region s may represent compensatory processes associated with attenuation of stuttering symptoms.