Excitation properties of peripheral nerves stimulated by an induced transverse electric field during magnetic stimulation.

Interest in magnetic stimulation (MS) of peripheral nerves has grown rapidly, but difficulties in determining excitation sites and computing the stimulation efficiency have prevented magnetic stimulation from becoming a routing clinical tool. The classical cable function has demonstrated that the activating function of nerves is the first spatial derivative of the electric field component parallel to the nerves. Therefore, excellent analyses have been presented in the literatures which predict the excitation properties, for peripheral nerves stimulated by the induced electric field component parallel to the nerves during MS. There is not, however, an adequate analysis for nerves excitation which considers the induced field component perpendicular to the fibers. Based on the improved cable function, which introduces a transverse field component, we have analyzed the excitation sites and the stimulation efficiencies during MS using round coils and 8-shaped coils, respectively. That is helpful to the further development of the functional magnetic nerve stimulation technique and to the clinical application of MS.