The activating function for magnetic stimulation derived from a three-dimensional volume conductor model

A three-dimensional volume conductor model of magnetic stimulation is proposed that relates transmembrane potential of an axon to the induced electric field in a uniform volume conductor. This model validates assumptions used previously to derive a one-dimensional cable model of magnetic stimulation (B.J. Roth and P.J. Basser, ibid., vol.37, p.588-97, 1990) of unmyelinated axons. The three-dimensional volume conductor model reduces to this one-dimensional cable equation forced by the activating function, - delta E/sub A//sup z// delta /sub z/.<
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