Objective: We aimed to elucidate neural representations in local field potentials (LFP) and single- and multi-unit activity of subthalamic nucleus (STN) neurons during speech tasks, providing insights into the neural dynamics underlying speech production in Parkinson’s disease (PD).

Background: The STN is primarily studied for motor control, but its role in speech processing is understudied. Speech impairments are common in PD (1), with some patients experiencing worsened dysarthria after deep brain stimulation (DBS) of the STN (2).

Method: We recorded unit activity and LFPs from micro and macro electrodes in 11 PD patients undergoing awake bilateral STN-DBS implantation surgery while they performed two speech tasks (sentence repetition, syllable repetition). Time-frequency analyses computed power within canonical bands (theta, alpha, beta, and low gamma). Power during the speech tasks was log-transformed and normalized to a pre-task baseline and averaged across trials. A linear mixed-effects model (LME) examined the effects of frequency band and task condition on mean normalized log power. A Poisson generalized linear model (GLM) assessed STN unit activity responsiveness to tasks.

Results: The LME analysis did not reveal significant effects of band, task, or their interaction on normalized log power. Unit analyses showed that 51% of clusters (23/45) showed significant modulation in firing rate during at least one task: 15% of clusters (7/45) responded to sentence production, 24% neurons (11/45) to syllable repetition, and 9% neurons (4/45) to both. In the subset of neurons that were not responsive to tasks we observed a significant negative correlation between baseline firing rate and improvement in UPDRS-III score.

Conclusion: LFPs and unit analyses can both be used to study STN dynamics or speech production. This study found less beta-band changes during speech compared to extant limb motor studies (3).  This suggests distinct STN mechanisms for speech control and highlights the importance of single-unit and multi-unit activity in understanding these dynamics.

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Table of Patient Information

References: 1. Rohl A, Gutierrez S, Johari K, Greenlee J, Tjaden K, Roberts A. Chapter 7 – Speech dysfunction, cognition, and Parkinson’s disease. In: Narayanan NS, Albin RL, editors. Progress in Brain Research [Internet]. Elsevier; 2022 [cited 2023 Sep 20]. p. 153–73. (Cognition in Parkinson’s Disease; vol. 269). Available from: https://www.sciencedirect.com/science/article/pii/S0079612322000176
2. Tröster AI, Jankovic J, Tagliati M, Peichel D, Okun MS. Neuropsychological outcomes from constant current deep brain stimulation for Parkinson’s disease. Mov Disord Off J Mov Disord Soc. 2017 Mar;32(3):433–40.
3. Mathiopoulou V, Lofredi R, Feldmann LK, Habets J, Darcy N, Neumann WJ, et al. Modulation of subthalamic beta oscillations by movement, dopamine, and deep brain stimulation in Parkinson’s disease. Npj Park Dis. 2024 Apr 5;10(1):1–7.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/single-and-multi-unit-activity-in-stn-provides-enhanced-insight-into-speech-related-neural-dynamics-in-parkinsons-patients/