Interplay Between Electrical Conductivity of Tissues and Position of Electrodes in Transcutaneous Spinal Direct Current Stimulation (tsDCS)

Abstract

AbstractTranscutaneous Spinal Direct Current Stimulation (tsDCS) is a neuromodulatory technique that applies low intensity (2–4 mA) direct currents to the spinal cord through electrodes placed above or near the vertebral column. As in transcranial electric stimulation, tsDCS induces an electric field in the spinal cord that can transiently change the transmembrane potential of spinal neurons or influence synaptic communication. Anatomical features near the electrodes or in the current path can originate local variations of the electric field magnitude and orientation that result in different effects generated at neuronal and synaptic level. Accurate realistic models of the spinal cord and surrounding tissues can provide a deeper understanding on how and why these variations occur.Our research aims at studying how electrode placement interacts with electrical conductivities of the tissues located in the current path. Using a realistic human model of the spinal cord and surrounding tissues, we estimated the electric field induced by tsDCS, considering different combinations of electrode positions and electrical conductivity of relevant tissues. Our study started from a homogeneous conductivity paradigm up to a full heterogeneous model. The results show that electrode placement influences the electric field orientation, while the conductivities of vertebral bone and CSF can lead to local electric field hotspots in spinal segments located in the current path. Understanding the interplay between these two effects can provide a solid framework to target specific spinal circuits in terms of magnitude and field orientation towards a more personalized approach.