A volume conductor study of compound action potentials of nerves in situ: the forward problem

A computer model for the stimulation of compound nerve action potentials, based on superposition of volume conducted single nerve fibre potentials, is presented. The model assumes that the intracellular fibre potential, the fibre diameter distribution and the electrical conductivities of different tissues are known. Volume conductor fields are calculated in the spatial frequency domain. The influence of important parameters in the model is evaluated numerically. It is shown that it is necessary to give up the usual assumption of homogeneity and isotropy in the extracellular medium. In the present model parameters are introduced which allow an overall description of the complex morphological and physiological structure of the nerve trunk. Simulation results indicate that the model is a rather promising tool in studying the main properties of compound action potentials which up till now have not been sufficiently well understood.