An efficient method and apparatus for magnetically stimulating the neural pathways of a higher level organism, namely the human body, is disclosed. The method includes selectively applying sinusoidally fluctuating electric power to a stimulator coil that overlies the neurons to be stimulated. The frequency of the power and, thus, the period of magnetic field produced by the coil is chosen to correspond to the time constant of the neurons to be stimulated. Realizable values fall in the range of 1.25 to 1.43 times the time constant of the neurons to be stimulated. The current and voltage of the applied power are in phase quadrature with the current lagging the voltage. During the first polarity (e.g., positive) excursion of the applied voltage, the magnetic field produced by the coil is insufficient to stimulate the underlying neurons, i.e., create a neuron depolarizing electric field. Rather, stimulation occurs during the second polarity (e.g., negative) excursion of the applied voltage. Preferably, coil current flow terminates at the end of the first current cycle. Alternatively, if restimulation during the third and subsequent polarity excursions of the applied voltage is desired, the coil current can be allowed to decay. The apparatus of the invention includes a series circuit comprising the stimulator coil 59 and a high voltage capacitor bank 57 connected in parallel with a power switch 55, across the output of a power supply 51. Closure of the power switch 55 results in the capacitor bank 57 being discharged through the coil 59 and the creation of the magnetic field that stimulates the underlying neurons. Efficiency is high because the resistance of both the capacitor discharge circuit and the power supply output are low. Further, because the resistance of the capacitor discharge circuit is low, discharge current flow is high, whereby an intense magnetic field is produced. Interlock circuits are provided to prevent the inadvertent operation of the apparatus. If desired, magnetic neuron stimulation can be enhanced simultaneously and/or sequentially by applying electric power to a pair of spaced-apart electrodes located in the vicinity of the coil.
Method and apparatus for magnetically stimulating neurons