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Dissertation
Activity in the human subthalamic nucleus during speech production
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Spring 2026
Abstract
The ability to communicate effectively is essential to participation in daily life, but any disruption in the neurological system can have a significant impact on a person’s ability to produce intelligible spoken language. Parkinson’s disease (PD) is among the most prevalent movement disorders in the world and negatively affects communication in 90% of those affected at some time in the course of the disease. Speech production relies on the highly precise coordination of muscles across articulatory, laryngeal, and respiratory subsystems while simultaneously processing and adapting to subtle acoustic and sensory feedback cues. In PD, motor symptoms are attributed to dysfunction of the basal ganglia, but it is unclear how basal ganglia pathology translates to the motor speech deficits (dysarthria) observed in PD. The subthalamic nucleus (STN) is a small nucleus in the basal ganglia that is highly impacted by PD. The role of the STN in speech production is not well understood. This study aimed to clarify the role of the STN in speech production through analysis of changes in single neuron activity in the STN during speech production and finger tapping tasks. It further sought to characterize the relationship between recording location and neural activity within the STN. From 84 participants with idiopathic PD undergoing implantation of deep brain stimulation in the STN, 294 neurons in the STN were isolated and analyzed for changes in firing rate. Using a combination of pre- and post-operative brain imaging, specific recording locations were identified and normalized to a standard template for group-level comparison.
STN neurons were modulated during both speech and finger tapping tasks but did not exhibit strong task-specific selectivity. Instead, modulation was primarily differentiated by temporal profile, with sustained activity observed during speech production and more transient responses during finger tapping. STN neurons contralateral to the body side with more severe PD symptoms were less likely to be task-modulated, suggesting that asymmetrical PD pathology is reflected in neural activity.
A novel interaction between disease duration, baseline firing rate, and biological sex was identified, indicating that disease-related changes in STN activity may differ across individuals. Follow-up analyses on behavioral speech data from a larger prospective study revealed that sex differences were also present in perceptual speech outcomes, suggesting a potential link between neural activity and functional communication deficits. Finally, spatial analyses of recording locations demonstrated evidence of lateralized and topographical organization within the STN, with speech-related modulation more frequently observed in the left nucleus and significant decreases in firing rate more common in the medial STN.
Together, these findings provide new insight into the organization and role of the STN in speech production, supporting STN contributions to continuous modulation and monitoring of motor output during complex behaviors such as speech. This work advances understanding of the neural mechanisms underlying speech impairment in PD and has implications for improving DBS targeting and programming to better preserve or enhance communication outcomes. It also highlights the importance of accounting for participant-specific characteristics in human electrophysiology.
Details
- Title: Subtitle
- Activity in the human subthalamic nucleus during speech production
- Creators
- Andrea Rohl
- Contributors
- Jeremy Greenlee (Advisor)Joel Berger (Advisor)Kirill Nourski (Committee Member)Jan Wessel (Committee Member)Nicholas Trapp (Committee Member)Mili Kuruvilla-Dugdale (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Neuroscience
- Date degree season
- Spring 2026
- Publisher
- University of Iowa
- Number of pages
- ix, 96 pages
- Copyright
- Copyright 2026 Andrea Rohl
- Language
- English
- Date submitted
- 04/27/2026
- Description illustrations
- illustrations (some color)
- Description bibliographic
- Includes bibliographical references (page 85-96).
- Public Abstract (ETD)
Speech production is a complex process that depends on the precise coordination of multiple brain and motor systems. Disruptions anywhere in this system can impair a person’s ability to produce clear, intelligible speech. Parkinson’s disease (PD), one of the most common movement disorders, affects communication in up to 90% of individuals over the course of the disease. Many of these difficulties are linked to abnormal activity in the basal ganglia, a group of brain structures involved in movement control. One key structure within this system, the subthalamic nucleus (STN), is strongly affected in PD, but its specific role in speech production remains unclear.
This study examined the activity of individual STN neurons in 84 people with PD during speech and simple finger movements. Neurons responded during both tasks, but differed in how they changed over time: speech was associated with more sustained activity, while finger movements produced brief responses. I also found that neural activity varied depending on disease duration, symptom side, baseline firing patterns, and biological sex.
Additional analyses showed that sex differences were also present in speech performance, suggesting a link between brain activity and communication outcomes. Finally, speech-related activity was more common in specific regions of the left STN.
Together, these findings suggest that the STN plays a role in continuously shaping and monitoring speech, with implications for improving treatments such as deep brain stimulation. Our findings additionally suggest that sex differences are not only present in the presentation and disease course of PD, but may also be present at the level of single neuron activity, with broad implications for work in human electrophysiology.
- Academic Unit
- Interdisciplinary Graduate Program in Neuroscience
- Record Identifier
- 9985177174602771
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