Electroencephalography and clinical neurophysiology. Supplement
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Electroencephalogr Clin Neurophysiol Suppl · Jan 1991
Mechanisms of peripheral nervous system stimulation using the magnetic coil.
We measured the distribution of the electric fields induced within isotropic and anisotropic volume conductors by figure '8' and round magnetic coils (MCs). For various MC orientations maximal electric fields were induced parallel to the inner surface of the volume conductor. Predictions from physical models roughly approximating human forearm and vertebral column were then tested by MC stimulation of distal median nerve at the wrist and nerve roots at the cervical spine, respectively. ⋯ This site most likely corresponds to the vicinity of the neuroforamina where the induced electric field is most intense and the first spatial derivatives peak. By contrast, the low value of the first derivative in the longitudinal axis of the vertebral canal implies that long tracts in the spinal cord are not likely to be excited using commercially available MCs. Our study also indicates that intracranial stimulation of facial nerve occurs at a selected low threshold location, probably reflecting focusing of induced current.