No Effect of Anodal tDCS on Motor Cortical Excitability and No Evidence for Responders in a Large Double-Blind Placebo-Controlled Trial.

Source: Brain Stimulation. 14(1):100-109, 2021 Jan-Feb.

Authors: Jonker ZD; Gaiser C; Tulen JHM; Ribbers GM; Frens MA; Selles RW

BACKGROUND: Transcranial direct current stimulation (tDCS) has emerged as a non-invasive brain stimulation technique. Most studies show that anodal tDCS increases cortical excitability. However, this effect has been found to be highly variable.

OBJECTIVE: To test the effect of anodal tDCS on cortical excitability and the interaction effect of two participant-specific factors that may explain individual differences in sensitivity to anodal tDCS: the Brain Derived Neurotrophic Factor Val66Met polymorphism (BDNF genotype) and the latency difference between anterior-posterior and lateromedial TMS pulses (APLM latency).

METHODS: In 62 healthy participants, cortical excitability over the left motor cortex was measured before and after anodal tDCS at 2 mA for 20 min in a pre-registered, double-blind, randomized, placebo-controlled trial with repeated measures.

RESULTS: We did not find a main effect of anodal tDCS, nor an interaction effect of the participant-specific predictors. Moreover, further analyses did not provide evidence for the existence of responders and non-responders.

CONCLUSION: This study indicates that anodal tDCS at 2 mA for 20 min may not reliably affect cortical excitability.