Cortical and subcortical underpinnings of typical and dysarthric speech - Resubmission - 1

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Project Summary/Abstract Individuals with motor speech disorders such as dysarthria are known to show aberrant phonatory and artic- ulatory precision, which can lead to reduced intelligibility when participating in social and vocational activities. Among the most common dysarthrias is that associated with Parkinson’s disease, which involves atypical online modulation of pitch (phonation) and formant frequencies (articulation). Despite high incidence of dysarthria, cog- nitive decline in this population may lead to a reduced capacity to engage actively with speech rehabilitation. The long-term goal of this research is to develop treatment approaches that tap into automatic pro- cesses to improve intelligibility in patients with dysarthria, including approaches that manipulate auditory feedback while applying neuromodulation to cortical regions. Toward this end, we leverage the availability of rare neurosurgical data (Electrocorticography in Epilepsy, Deep Brain Stimulation in Parkinson’s disease) to map out the cortical substrates of phonatory and articulatory control while accounting for the role of subcortical structures. According to prominent models of speech production, deficits in speech motor control are a reflection of ab- normalities in motor circuits spanning cortical and subcortical structures. Experimental perturbation of real-time auditory feedback concurrent with neuroimaging has advanced the current understanding of the cortical under- pinnings for typical incorporation of auditory feedback into speech output (“sensorimotor control”). Meanwhile, investigations of sensorimotor control in patients with Parkinson’s disease have helped elucidate the role of the subthalamic nucleus within the cortical-subcortical motor circuit in atypical sensorimotor control. Some past stud- ies have suggested that pitch and formants are differentially modulated in distinct subregions within premotor cortex, and within the subthalamic nucleus. However, discrepancies across studies have prevented the robust parcellation of cortical and subcortical structures for the specialized control of distinct acoustic features. To pinpoint the neural mechanisms underlying typical feedback-based sensorimotor control, Aim 1 maps out cortical activity associated with compensatory responses to perturbations of pitch and formants using electrocorticography in patients with Epilepsy. To isolate the subthalamic nucleus’s role in sensorimotor con- trol, Aim 2 compares compensatory responses to perturbations of pitch and formants in healthy controls versus patients with Parkinson’s disease in conditions with Deep Brain Stimulation ON versus OFF. The proposed experimental paradigm is significant in that it will clarify conflicting reports about the specializa- tion of cortical and subcortical structures in sensorimotor control of pitch versus formants. Evidence for the effects of neurosurgery on speech outcomes in common motor disorders could directly inform perioperative decisions in clinical care. This research will have direct applications for the future development of neuromodulation to enhance speech treatment for patients with Parkinson’s disease. Results could also inform treatments for a range of motor speech disorders, ultimately maximizing phonatory and articulatory control to improve patient communication.