Degree
Doctor of Philosophy (PhD)
Department
Communication Sciences and Disorders
Document Type
Dissertation
Abstract
Speech is a goal-directed and complex sensorimotor behavior relying on timely and precise sequences of neural, cognitive and motor processes. From planning articulatory musculatures and vocal gestures to coordinating respiration and phonation, a distributed network of cortical and subcortical regions is involved in transforming a linguistic intention into a vocal output. Among these regions, supplementary motor area (SMA) acts as a neural interface that is associated with planning, initiating, timing, coordinating, and executing internally generated speech. SMA dysfunction is implicated in several disorders characterized with disrupted speech motor control, such as Parkinson’s disease, apraxia of speech, and stuttering. Its anatomical accessibility and integrative role make SMA a promising neuromodulation target for exploring and optimizing speech motor networks. Transcranial electrical stimulation (tES) – including high-definition transcranial alternating current stimulation (HD-tACS), transcranial random noise stimulation (tRNS), and direct current stimulation (HD-tDCS) – is a non-invasive and well-tolerated technique that modulates neural excitability by applying weak currents over the scalp within research and clinical settings. The effects of several tES protocols over the SMA were examined across two age groups (young and older adults) in the context of speech production. The results showed that the SMA-targeted stimulation can improve speech motor planning and timing, with the modulation effects varying based on the stimulation protocol, network state, oscillatory dynamics, and, importantly, age. This body of work was an attempt to move from a theoretical framework underlying the role of the SMA, to probing the causal mechanisms of distinct stimulation protocols, personalizing the stimulation parameters based on task-specific demands, examining age-related modulatory effects, and ultimately advancing toward translational application across lifespan.
Date
7-8-2026
Recommended Citation
Tabari, Fatemeh, "Age-Related Modulation of Speech Motor Network Using Personalized Beta-Band HD-tACS over the Left SMA" (2026). LSU Doctoral Dissertations. 7148.
https://repository.lsu.edu/gradschool_dissertations/7148
Committee Chair
Johari, Karim
LSU Acknowledgement
1
LSU Accessibility Acknowledgment
1