Transcranial direct current stimulation over the primary motor cortex improves speech production in post-stroke dysarthric speakers: A randomized pilot study

Min Ney Wong; Faisal Nouman Baig; Yeuk Ki Chan; Manwa L Ng; Frank F Zhu; Joseph Shiu Kwong Kwan

doi:10.1371/journal.pone.0275779

Transcranial direct current stimulation over the primary motor cortex improves speech production in post-stroke dysarthric speakers: A randomized pilot study

PLoS One. 2022 Oct 13;17(10):e0275779. doi: 10.1371/journal.pone.0275779. eCollection 2022.

Authors

Min Ney Wong^{1

2

3}, Faisal Nouman Baig^{1

2

3}, Yeuk Ki Chan⁴, Manwa L Ng⁴, Frank F Zhu⁵, Joseph Shiu Kwong Kwan⁶

Affiliations

¹ Department of Chinese and Bilingual Studies, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong.
² Research Institute for Smart Ageing, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong.
³ Research Centre for Language, Cognition, and Neuroscience, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong.
⁴ Speech Science Laboratory, Faculty of Education, The University of Hong Kong, Pokfulam, Hong Kong.
⁵ HealthyMind Neuro-Wellness Centre, Central, Hong Kong.
⁶ Department of Brain Sciences, Faculty of Medicine, Imperial College London, London, United Kingdom.

Abstract

Purpose: The current study investigated the therapeutic potential of transcranial direct current stimulation (tDCS) on speech intelligibility, speech-related physiological and vocal functions among post-stroke dysarthric patients.

Method: Nine chronic post-stroke dysarthric patients were randomly assigned to the stimulation or sham group. The stimulation group received 2mA of anodal tDCS over the left inferior primary motor cortex for 15 minutes, while the sham group received 30s of stimulation under the same settings. All the participants received 10 daily 15 minutes of individualized speech therapy targeting their dominant phonological process or phonemes with the greatest difficulty. The outcome measures included (1) perceptual analysis of single words, passage reading and diadochokinetic rate, (2) acoustic analysis of a sustained vowel, and (3) kinematic analysis of rapid syllable repetitions and syllable production in sentence, conducted before and after the treatment.

Results: The results revealed that both the stimulation and sham groups had improved perceptual speech intelligibility at the word level, reduced short rushes of speech during passage reading, improved rate during alternating motion rate, AMR-kha1, and improved articulatory kinematics in AMR-tha1 and syllables /tha1/ and /kha1/ production in sentence. Compared to the sham group, the stimulation group showed significant improvement in articulatory kinematics in AMR-kha1 and syllable /kha1/ production in sentence. The findings also showed that anodal stimulation led to reduced shimmer value in sustained vowel /a/ phonation, positive changes in articulatory kinematics in AMR-tha1 and syllables /pha1/ and /kha1/ production in sentence at the post treatment measure. In addition to positive effects on articulatory control, reduced perturbation of voice amplitude documented in the stimulation group post treatment suggests possible tDCS effects on the vocal function.

Conclusions: The current study documented the beneficial effects of anodal tDCS over the primary motor cortex on speech production and suggested that combined tDCS and speech therapy may promote recovery from post-stroke dysarthria.

Publication types

Randomized Controlled Trial
Research Support, Non-U.S. Gov't

MeSH terms

Humans
Motor Cortex*
Pilot Projects
Speech Intelligibility
Stroke* / complications
Stroke* / therapy
Transcranial Direct Current Stimulation* / methods

Grants and funding

The study was unable to secure funding for its implementation and data collection. Later M. N. Wong received grant supports from the Research Grants Council Early Career Scheme (Grant Number 25609819) (https://www.ugc.edu.hk/eng/rgc/) and The Hong Kong Polytechnic University (Project Code: G-YBZN) (https://www.polyu.edu.hk/rio/) to support the data analysis and writing up of the study. The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.