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Department of Neurology
Paul J. Maccabee, M.D.
Professor of Neurology
Director of EMG Laboratory
SUNY Downstate Medical Center, Brooklyn, NY
Since the early 1980s it has been possible to employ magnetic induction to excite the peripheral and central nervous system of intact humans in health and disease. One area of intense investigation has been to determine where stimulation takes place in relation to the geometry, orientation, and location of the magnetic coil, and the optimal shape, duration and topography of the induced electric field. Major advances in understanding identified in my laboratory were based on fundamental studies of in-vitro physical models, and facial, wrist, cervical spine, and lumbosacral spine stimulation studies in the human. In-particular, loci of nerve depolarization were found to occur at selected “low threshold sites” including a bend in a nerve and at neuroforamina. Further, low threshold sites were optimally excited at the peak of the induced electric field, for example at the center of the long axis of the junction of a figure-of eight magnetic coil (and not at the spatial derivative of the induced electric field). The conclusions also extrapolate to stimulation theories of the CNS. Unexpectedly, the application of these fundamental principles resulted in creation of a new method to neuromagnetically excite rostral and caudal cauda equina in patients with peripheral neuropathy. In a study of 88 patients, upper leg conduction time (from distal cauda equina to popliteal fossa) uniquely distinguished demyelinating neuropathies.