Modulation of speech performance during tongue twister production using non-invasive transcranial direct current stimulation (tDCS)

Abstract

Introduction: Neuromodulation of the brain has received increasing attention and interest in recent years. Research showed that transcranial direct current stimulation (tDCS) has modulatory effect on cognitive functions and motor behavior in both normal and brain-damaged individuals. This study aimed to examine the possible effect of tDCS in enhancing articulatory skills during tongue twister production task in healthy individuals. Method: Fifteen native Cantonese speaking adults aged between 19 to 52 years with no history of speech or language disorders, brain surgery, seizure or stroke were recruited for the study. A list of 21 Cantonese tongue twisters was selected as stimuli. The participants were asked to produce the tongue twisters as fast and accurately as possible 15 minutes before tDCS (pre), immediately after tDCS (post 1) and 4-hour after tDCS (post 2). During the tDCS stimulation, a mild direct current of 2 mA was delivered to each participant using a constant direct current stimulator via saline-soaked sponge electrodes for 15 minutes. The anodal and cathodal electrodes were placed over the Broca’s area (F5) and the contralateral frontopolar cortex, respectively. Results: Preliminary findings showed positive effects of tDCS on vocal reaction time and rate of tongue twisters production immediately after the stimulation, with no significant difference between post1 and post2 measurements. No stimulation effects was reported for articulation accuracy of tongue twisters production. Conclusion: Anodal tDCS over the left frontal region including Broca’s area (F5) can enhance the rate and reaction time of tongue twister production and the effect was maintained immediately after the stimulation.