A computational model of tsDCS effects in SOD1 mice: from MRI-based design to validation

During trans-spinal direct current stimulation (tsDCS) the transmembrane potential of neurons is modified by an electric field (EF) induced due to externally applied direct current (DC). The resultant functional effects are being harnessed in the treatment of various neurological conditions; however, the fundamental mechanisms of action underlying tsDCS remain unclear. This ambiguity is largely attributed to the limited knowledge of the geometrical constraints of the EF in the polarized spinal regions. It is, then, essential to develop tools that enable researchers to plan tsDCS approaches in a controlled and systematic manner, ensuring the reproducibility of stimulation effects at spinal targets. With this paper, we aim to provide a comprehensive computational model of tsDCS intervention in mice to support further fundamental research in this area. Our model was constructed using high-resolution MRI scans of C57/B6 mice, which were segmented and reconstructed into a realistic mouse computational model. In vivo electrophysiological measurements of voltage gradients in SOD1 G93A mice were used to validate our model predictions in real-life scenarios. In both the modeling and in vivo studies, we employed a rostrocaudal arrangement of DC electrodes to replicate stimulation parameters that have proven effective for modulating murine spinal circuits. Both the computational and in vivo approaches yielded highly consistent results, with EF parameters primarily influenced by the distance between the target site and the tsDCS electrodes. We conclude that this developed model offers high accuracy in EF distribution and can significantly substantiate basic research in tsDCS.