The excitation functional for magnetic stimulation of fibers.

Threshold problems in electric stimulation of nerve and muscle fibers have been studied from a theoretical standpoint using the excitation functional. Here the excitation functional is extended to magnetic stimulation of excitable nerve and muscle fibers. A unified derivation of the functional is done, for (non myelinated) nerve and muscle fibers, by means of the nonlinear cable equation with a Fitzhugh-Nagumo membrane model and a generalized Rattay's activating function. The identification problem of the excitation functional for magnetic stimulation, from strength-duration experimental data, is briefly considered.