Investigation The Effect of Conventional Vs. Individualized tDCS Intensity to Achieve Uniform E-Fields

Background: Replications of studies employing transcranial direct stimulation (tDCS) shows great variations in physiological and behavioral outcomes. The disparity between studies is based on the expectations of getting the same cortical activity changes consistently once the procedures and current parameters have been repeated. Nevertheless, this assumption was inoperative, due to the individualized variations of numerous parameters such as: age, disease type, symptom severity, head geometry, etc. Objective: Through this clinical trial we aim to reduce the variability of the physiological and behavioral outcomes of tDCS by individualizing the current intensity and to study the neurophysiological and behavioral outcome differences between participants who receive the customized current intensity in comparison to the others who would receive a fixed dose. Methods: Based on individual patient's structural MRI images, the Electrical field (E-field) distribution can be modeled and the individualized current dose to stimulate a target region can be determined. A group of thirty persons with multiple sclerosis (PWMS) would be pseudo-randomized into three groups receiving all 3 treatments of individualized tDCS, fixed currents (2 mA), and sham tDCS. Baseline and post-intervention assessment of physiological and behavioral outcome measures will be assessed using respectively, transcranial magnetic stimulation (TMS) recruitment curve and a stop-signal task and GO/No-go test. Significant statement and clinical relevance: Individualizing the patient's tDCS current intensity will result in a better clinical outcome (i.e. more robust physiological and behavioral effects), as compared to a tDCS application that is based on a fixed current.