Finite Element Analysis of Action Potential Generation in the Cortico-Spinal Tract During Transcranial Electrical Stimulation

Transcranial Electrical Stimulation (TES) is an important procedure in intraoperative motor monitoring. When neurosurgery is performed at certain difficult locations within the central nervous system (CNS), TES evaluates CNS functions during surgical manipulations to prevent post-operative complications. In TES, electrical stimulation is provided to the motor cortex through electrodes placed on the scalp, generating action potentials (APs) which travel through the nervous system. Although TES is in widespread use, the sites of AP generation within the brain, particularly with respect to the parameters of stimulation, are not well understood. We have constructed a finite elements model to analyze TES elicited neuron activation based on a 3D volume conductor model. A simulation domain is constructed with inhomogeneous electrical conductivity values for different tissues and a model of the Cortical-Spinal Tract (CST) is created through Diffusion Tensor Imaging (DTI). Laplace´s equation is numerically solved with a set of appropriately selected boundary conditions using the finite element method. Our simulation has yielded clear results of both electric potential and field distributions along the CST, providing valuable information on the mechanism of TES-elicited neuron activation.