A PET STUDY OF THE NEURAL SYSTEMS OF STUTTERING

THE cause of stuttering is unknown(1). Failure to develop left-hemisph eric dominance for speech is a long-standing theory(1) although others implicate the motor system more broadly(2), often postulating hyperac tivity of the right (language nondominant) cerebral hemisphere(3). As knowledge of motor circuitry has advanced(4), theories of stuttering h ave become more anatomically specific, postulating hyperactivity of pr emotor cortex, either directly(5) or through connectivity with the tha lamus and basal ganglia(6), Alternative theories target the auditory(7 ) and speech productions(8,9) systems. By contrasting stuttering with fluent speech using positron emission tomography combined with chorus reading to induce fluency, we found support for each of these hypothes es, Stuttering induced widespread over-activations of the motor system in both cerebrum and cerebellum, with right cerebral dominance. Stutt ered reading lacked left-lateralized activations of the auditory syste m, which are thought to support the self-monitoring of speech, and sel ectively deactivated a frontal-temporal system implicated in speech pr oduction, Induced fluency decreased or eliminated the overactivity in most motor areas, and largely reversed the auditory-system underactiva tions and the deactivation of the speech production system. Thus stutt ering is a disorder affecting the multiple neural systems used for spe aking.