Cortical Excitability through Anodal Transcranial Direct Current Stimulation: a Computational Approach.

The present study analyzes the effect of various anodal transcranial direct current stimulation (tDCS) configurations in terms of electric field and voltage distribution. The work aims to assess the role of tDCS configurations considering subject's specific anatomy in a computational framework. The study considers the effect of conventional and high definition transcranial direct current stimulation (HD-tDCS) by using synthetic magnetic resonance image (MRI) volumes for normal brain and brain with multiple sclerosis (MS) lesions. The configurations presented in this study compare the effect of various m x n HD-tDCS and conventional tDCS on standard Montreal Neurological Institute (MNI152) head model which is a T1 MRI volume obtained by averaging 152 individuals at 1 mm3 resolution. The study evaluates the role of disc, ring, and pad electrodes in various configurations of tDCS application. The approximate surface area for each electrode in HD-tDCS application considered in the study is 113 mm2. The significant difference in voltage distribution has been observed due to 1 × 1 HD-tDCS configuration on synthetic MRI of normal and lesion brain using disc and ring electrodes. For region specific approach, outer ring structured electrode configuration - an extended m x n HD-tDCS configuration is presented in this study. The proposed outer ring HD-tDCS configuration has been compared with m × 1 and m × 2 HD-tDCS configurations with different types of electrodes in terms of focality, induced electric field and voltage generated. On the basis of the insights gained from the analysis of various tDCS configurations on standard, normal and lesion structural data, the design of HD-tDCS as a tool in neuro-rehabilitation has been proposed. This computational model approach is useful in fixing various parameters of current stimulation: intensity, type and arrangement of electrodes and target region by using structural MRI data of an individual prior to the real stimulation in clinical trials.