Magnetic stimulation of axons in a nerve bundle: Effects of current redistribution in the bundle
- 78 Downloads
Recently, we developed a model of magnetic stimulation of a concentric axon in an anisotropic nerve bundle. In that earlier paper, we considered a single axon surrounded by a nerve bundle represented as a homogeneous anisotropic monodomain medium. In this paper we extend our previous calculations to examine excitation of axons within a nerve bundle without neglecting the presence of other axons in the nerve bundle. A three-dimensional axial symmetry volume conductor model is used to determine the transmembrane potential response along an axon due to induced electric fields produced by a toroidal coil. Our principal objective is to examine the effect of current redistribution to other axons in the bundle on excitation characteristics. We derive the transmembrane potential along an axon for two currently available models of current redistribution: the biodomain model and the spatial-frequency monodomain model. Results indicate that a reduction in the transmembrane potential along an axon due to the presence of other nerve fibers in the bundle is observed. Axons located at the periphery of a nerve bundle have lower thresholds and different excitation sites compared with axons located near the center of a nerve bundle.
KeywordsMagnetic Stimulation Electrical stimulation Anistropy Coils Transmembrane response Nerve Bundle Perineurium Sheath Bidomain Spatial-frequency conductivity Monodomain Cable Equation Volume conductor effects
Unable to display preview. Download preview PDF.
- 6.Chokroverty, S. E. Magnetic Stimulation in Clinical Neurophysiology. Stoneham, MA: Butterworth, 1990.Google Scholar
- 9.Clark, J. W., E. C. Greco, and T. L. Harman. Experience with a Fourier method for determining the extracellular potential fields of excitable cells with cylindrical geometry.CRC Crit. Ref. Bioeng. 1–22, 1978.Google Scholar
- 11.Durand, D., and S. S. Nagarajan. Theoretical and experimental aspects of magnetic nerve stimulation. In: Proc. 14th Annu. Int. Conf. IEEE-EMBS, Vol. 4, 1992, pp. 1406–1407.Google Scholar
- 12.Durand, D., A. S. F. Ferguson, and T. Dalbasti. Effects of surface boundary on neuronal magnetic stimulation.IEEE Trans. Biomed. Eng. 37:588–597, 1992.Google Scholar
- 14.Jackson, J. D. Classical Electromagnetism, Second edition. New York: John Wiley & Sons, 1975.Google Scholar
- 15.Maccabee, P. J., V. E. Amassian, L. Eberle, A. P. Rudell, and R. Q. Cracco. The magnetic coil activates amphibian and primate nerve in-vitro at two sites and selectively at a bend.J. Physiol. 446:208P, 1992.Google Scholar
- 16.Nagarajan, S. S., and D. M. Durand. Analysis of magnetic stimulation of a concentric axon in a nerve bundle. In: Proc. 15th Int. IEEE EMBS Conf. Vol. III, 1993, pp. 1429–1430.Google Scholar
- 17.Nagarajan, S. S., and D. M. Durand. Analysis of magnetic stimulation of a concentric axon in a nerve bundle.IEEE Trans. Biomed. Eng. 1994, in press.Google Scholar
- 19.Nilsson, J., M. Panizza, B. J. Roth, P. J. Basser, L. G. Cohen, G. Caruso, and M. Hallett. Determining the site of stimulation during magnetic stimulation of a peripheral nerve.Electroencephol. Clin. Neurophysiol. 85:4:253–264, 1992.Google Scholar
- 23.Roth, B. J., F. L. H. Gielen, and J. P. J. Wikswo. Spatial and temporal frequency-dependent conductivities in volume-conduction calculations for skeletal muscle.Math. Biosci. 88:159–189, 1988.Google Scholar