Effects of cerebellar transcranial direct current stimulation (tDCS) on motor skill learning in swallowing

Abstract

Objective This study evaluated the effects of cerebellar tDCS on motor learning for swallowing. Methods In a double-blind RCT, 39 healthy adults received either sham, anodal tDCS, or cathodal tDCS in two sessions on two consecutive days. Following 20 min cerebellar tDCS (2 mA) or sham, they underwent swallowing skill training that targeted control of timing and magnitude of submental muscle activation during swallowing. Linear mixed models were used to identify the effects of stimulation on timing and magnitude accuracy as measured by the change in task performance for each training session, and for skill retention on days 3 and 10 post-intervention. Results Only the sham group had a reduced temporal error from baseline to all following timepoints. When compared to error changes in the sham group, changes from baseline in temporal errors were higher at all timepoints post-intervention for the anodal group, and higher at both retention assessments for the cathodal group. Amplitude errors were smaller for all conditions at all timepoints post-intervention compared to baseline. Conclusions Cerebellar tDCS was found to inhibit temporal aspects of motor skill learning in swallowing. For the tDCS parameters used in this study, there is no support for use of tDCS to facilitate swallowing rehabilitation. Trial Registry Number (https://www.anzctr.org.au/): ACTRN12615000451505. IMPLICATIONS FOR REHABILITATION Cerebellar tDCS, in combination with motor skill training, has been demonstrated to increase motor skill learning in healthy individuals and neurologically impaired patients. In this study, cerebellar tDCS applied prior to swallowing skill training adversely affected timing measures of submental muscle activation during swallowing. In contrast to published outcomes in the corticospinal literature, both anodal and cathodal tDCS resulted in a relative inhibitory effect on motor skill learning in swallowing when compared to the sham condition. Swallowing skill training without tDCS produced increased accuracy in outcomes.