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Cerebellar tDCS Improves Speech Reaction Time During Syllable Sequencing in Healthy Aging
Poster Session A, Wednesday, September 30, 11:00 am - 1:00 pm, Wangari Maathai
Mehdi Bakhtiar1, Maria Teresa Carthery1; 1The University of Hong Kong
Background: Aging is associated with declines across multiple neurocognitive systems. Several studies have reported subtle but measurable age-related changes in speech motor control, including slower speech rate, reduced accuracy during complex syllable sequencing, longer movement durations, and greater temporal variability (Bilodeau-Mercure et al., 2015; Hu et al., 2023; Tremblay et al., 2018), as well as slower speech reaction times in response to temporally unpredictable cues compared with younger adults (Johari et al., 2019). The cerebellum, through its connections with cortical speech-motor regions, plays a central role in maintaining fluent, precisely timed speech, particularly under conditions requiring sequencing, adaptation, or rapid error correction. Although non-invasive cerebellar stimulation has been proposed to enhance speech production, evidence remains limited, task-dependent, and rarely focused on aging populations. This study addressed this gap by examining the effects of multi-session anodal cerebellar transcranial direct current stimulation (tDCS) on speech motor performance in older adults. Methods: Fourteen Cantonese-speaking older adults aged 60 years or above, with MoCA scores between 25 and 30, completed two phases of three training sessions. Each session involved 20 minutes of 2 mA anodal or sham tDCS over the right posterolateral cerebellum, combined with cognitive-linguistic and motor speech training in a randomized, double-blind, sham-controlled crossover design. Outcome measures included diadochokinetic (DDK) reaction time and speech rate, as well as tongue-twister speech rate and articulatory accuracy. Data were analyzed using linear mixed-effects models. Results: Significant condition-by-time interactions were observed across selected outcome measures (p < .001). For the DDK task, reaction time improved only following anodal stimulation compared with sham stimulation. Although DDK speech rate increased in both conditions, the effect reached significance only under sham stimulation. No significant stimulation-related effects were found for tongue-twister speech rate or articulatory accuracy. Conclusion: The results of this small-scale trial suggest that right cerebellar anodal stimulation may reduce age-related decline in speech motor timing, possibly by enhancing compensatory recruitment of the cerebellum and its connected speech-motor networks (Johari et al., 2019). The findings support the cerebellum’s role in speech motor planning and temporal control, while indicating that stimulation effects may be outcome-specific and more evident for preparatory timing than for execution timing or articulatory accuracy. Replication with larger samples, more frequent stimulation sessions, and sensitive speech motor outcomes is warranted. References: Bilodeau-Mercure, M., Kirouac, V., Langlois, N., Ouellet, C., Gasse, I., & Tremblay, P. (2015). Movement sequencing in normal aging: speech, oro-facial, and finger movements. AGE, 37(4), 78. Hu, H., Li, J., He, S., Zhao, Y., Liu, P., & Liu, H. (2023). Aging-related decline in the neuromotor control of speech production: current and future. Frontiers in Aging Neuroscience, 15, 1172277. Johari, K., Ouden, D.-B. den, & Behroozmand, R. (2019). Behavioral and neural correlates of normal aging effects on motor preparatory mechanisms of speech production and limb movement. Experimental Brain Research, 237(7), 1759–1772. Tremblay, P., Deschamps, I., Bédard, P., Tessier, M.-H., Carrier, M., & Thibeault, M. (2018). Aging of Speech Production, From Articulatory Accuracy to Motor Timing. Psychology and Aging, 33(7), 1022–1034.
Topic Areas: Speech Motor Control, Speech-Language Treatment