Computational models of non-invasive brain and spinal cord stimulation.

Non-invasive brain and spinal cord stimulation techniques are increasingly used for diagnostic and therapeutic purposes. Knowledge of the spatial distribution of the induced electric field is necessary to interpret experimental results and to optimize field delivery. Since the induced electric field cannot be measured in vivo in humans, computational models play a fundamental role in determining the characteristics of the electric field. We produced computational models of the head and trunk to calculate the electric field induced in the brain and spinal cord by transcranial magnetic stimulation, transcranial direct current stimulation and transcutaneous spinal cord direct current stimulation. The field distribution is highly non-uniform and depends on the type of technique used, on the position of the stimulation sources, and on anatomy. In future these models may be improved by using more accurate and precise values for the physical parameters as they become available, by combining them with neuronal models to predict the outcome of stimulation, and by better segmentation and meshing techniques that make producing individual models practicable.