Magnetic Stimulation of the Spinal Cord: Evaluating the Characteristics of an Appropriate Stimulator

This article aims to determine the necessary characteristics of a magnetic stimulator, capable of stimulating neural tracts of the spinal cord in a healthy subject. Our previous preliminary tests had shown that the commercial clinical magnetic stimulator Magstim Rapid(2) was unable to reach excitable structures within the spinal cord, and only adjacent spinal nerves could be activated with the maximal deliverable field strength. In a subsequent modeling study, we were able to show that the figure eight-shaped commercial coil could be one reason for, in this particular application, insufficient reach of the magnetic field, and substantial improvements could be gained by alternative geometrical arrangement of the windings of the magnetic coils. A further outcome was that a substantially higher driving voltage for the coil would be necessary to achieve activation of neural tracts within the spinal cord.