The Role of Cerebellum in Speech

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.

Inclusion criteria

• Diagnosis of cerebellar ataxia (CA) resulting from degeneration of the cerebellum AND normal hearing abilities OR
• Healthy volunteers with no known history of physical or neurological abnormalities AND normal speech, hearing, and reading abilities
• For some studies, primary language of American English may be required

Exclusion criteria

for healthy volunteers:

• Neurological impairment or psychiatric illness

Exclusion criteria

for participants with cerebellar ataxia (CA):

• Neurological impairment or psychiatric illness apart from those arising from cerebellar damage

Exclusion criteria

for participants with CA or for healthy volunteers participating in MRI (may still be eligible for other study procedures):

• Any contraindication to participating in an MRI study including the following: implanted metallic parts or implanted electronic devices, including pacemakers, defibrillators, stimulators, or implant medication pump, or nonremovable piercings; aneurysm clip or other metal in the head (except mouth); claustrophobia precluding MRI

Exclusion criteria

for healthy volunteers participating in TMS (may still be eligible for other study procedures):

• Any contraindications to participating in a TMS study including the following: epilepsy, use of certain medications, heart disease, and pregnancy; scalp wounds or infections; any other contraindication discovered during screening procedures
• Any contraindication to participating in an MRI study including the following: implanted metallic parts or implanted electronic devices, including pacemakers, defibrillators, or implant medication pump, or nonremovable piercings; claustrophobia precluding MRI

Exclusion criteria

for all potential participants:

• Pregnant or trying to become pregnant (may still be eligible for behavioral studies only)
• History of alcohol abuse, illicit drug use or drug abuse or significant mental illness
• Hypertensive or hypotensive condition
• Any condition that would prevent the subject from giving voluntary informed consent
• Enrolled or plans to enroll in an interventional trial during this study
• Ongoing seizures that are not well controlled despite medication
• Use of hearing aid or other device to improve hearing