This study will investigate the how the cerebellum is involved in speech motor learning over time and short-term corrections in patients with cerebellar ataxia and healthy controls. This will be accomplished through three approaches: behavioral studies, magnetic resonance imaging (MRI), and transcranial magnetic stimulation (TMS). During behavioral studies, participants will be asked to speak into a microphone while their voice is played back over earphones, and to do other speaking tasks. MRI will be acquired to perform a detailed analysis on brain function and anatomy related to speech and the cerebellum. In healthy controls, TMS will also be performed to temporarily disrupt the cerebellum before, during, or after the participant performs speaking tasks. Patients with cerebellar ataxia and healthy volunteers will be asked to complete behavioral studies and/or MRI; healthy volunteers may be asked to additionally participate in TMS.
This study will investigate the role of the cerebellum in speech, building upon prior work in understanding cerebellar function in reaching and walking. Neuroimaging and lesion studies have provided strong evidence that the cerebellum is an integral part of the speech production network, though its precise role in the control of speech remains unclear. Furthermore, damage to the cerebellum (either degenerative or focal) can lead to ataxic dysarthria, a motor speech disorder characterized, in part, by impaired articulation and severe temporal deficits. This project seeks to bridge the gap between theoretical models of cerebellar function and the speech symptoms associated with ataxic dysarthria. Two mechanisms underlie speech motor control - feedback and feedforward control. In feedback control, speakers use sensory feedback (e.g., of their own voice) to control their speech. In feedforward control, speakers use knowledge gained from their past speech productions, rather than on-line feedback, to control their speech. This study entails a systematic plan to elucidate the role of the cerebellum in feedforward and feedback control of speech. A central hypothesis is that the cerebellum is especially critical in the feedforward control of speech, but has little involvement in feedback control. To explore this hypothesis, we will obtain converging evidence from three innovative methodologies: 1) Neuropsychological studies of speech-motor responses to real-time altered auditory feedback in patients with cerebellar atrophy (CA) and matched healthy controls, 2) Parallel studies in healthy controls undergoing theta-burst transcranial magnetic stimulation to create "virtual lesions" of the cerebellum, and 3) Structural and functional studies in CA patients to examine the relationship between cerebellar lesion location, dysarthria symptoms, and feedforward and feedback control ability.
Speech provides an important opportunity to examine how well current theories of cerebellar function generalize to a novel effector (vocal tract) and sensory (auditory) domain. Its purpose for communication imposes exacting spectro-temporal constraints not seen in other motor domains. Furthermore, the distinctive balance of feedback and feedforward control in speech allows us to examine changes in both control types subsequent to cerebellar damage. Critically, this is the first work examining the link between theoretically motivated control deficits in CA patients and the speech symptoms associated with ataxic dysarthria, as well as their neural correlates.
