Capacitive stimulatory effect in magnetic stimulation of nerve tissue

Two related contactless stimulating methods were examined using frog nerve-muscle preparations. One stimulates the nerve by means of voltage pulses through windings on a permalloy core through which the nerve bundle is threaded. The pulse strength-duration curve was measured, and found to give at chronaxy of 20 μsec, which is shorter by one decade than the 0.3 msec for galvanic stimulation. The other method excites the nerve by means of a high-frequency magnetic field generated in the airgap of a ferrite core driven by burst signals. The voltage threshold for nerve excitation was minimum near 1 kHz. These phenomena are explained by an equivalent circuit of the magnetic circuit and nerve bundle.