P165 Variability and stability in response to 2 mA transcranial Direct Current Stimulation (tDCS)

Abstract

Introduction Repeated application of tDCS has been found to induce prolonged changes in cortical excitability. This has led to interest into the techniques therapeutic potential and a range of promising findings. However, there remain a number of unexplored issues, including the high level of individual variability often found in response to tDCS ( Wiethoff et al., 2014 ). Objectives The study aimed to investigate inter and intra-subject variability in response to 2 mA anodal, and cathodal tDCS. Method Ten subjects participated in four testing sessions for both anodal and cathodal stimulation respectively. Nine participants also completed two sessions of sham stimulation. Various TMS techniques including Input–Output (IO) curves were used to measure change in cortical excitability. Results Large inter-subject variability was apparent for all conditions; however, group analysis of IO curve changes revealed that anodal tDCS significantly increased excitability (Fig. 1), whereas cathodal (Fig. 2) and sham failed to have any significant effects. Analysis of intra-subject changes in cortical excitability across the four sessions revealed poor reliability for both anodal and cathodal stimulation. Reliability in the sham condition was fair. Conclusions The findings have important implications for the use of tDCS in research and therapeutic contexts. In particular the findings suggest that group level analysis may mask substantial differences occurring at an individual level. The finding that cathodal tDCS did not significantly alter cortical excitability at a group level, and that the effects were not stable within participants suggests particular caution is warranted when using these parameters to modulate cortical excitability. Download : Download high-res image (308KB) Download : Download full-size image Download : Download high-res image (274KB) Download : Download full-size image