Computer simulation of corticospinal activity during transcranial electrical stimulation in neurosurgery

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 which travel through the nervous system. Despite widespread use, the sites of activation (AP generation) within the brain are not well understood. We have integrated computational and neurophysiologic models including a 3D volume conduction head model computed using the finite element method, a realistic corticospinal tract (CST) model, and a geometry-specific axon activation model for the CST to predict the sites of activation along the CST as a function of electrode placement and stimulation voltage, which have been verified by epidural recordings. We then develop a simple meshing and rendering algorithm to display the activating function along the CST. We have found that the AP generation appears closely linked to regions of high CST curvature. Our model and rendering algorithm provide a window to visualize the effects of TES in the brain.