The D190 generates a high-intensity magnetic field pulse that can, for example, stimulate the human cerebral cortex for the recording of motor-evoked potentials. Because the ratio of surface skin current to deep nerve stimulus current is reduced compared to the ratio resulting from attaching electrodes to the scalp, the D 190 is not painful for the subject. The D190 operates noninvasively by rapidly changing the magnetic field produced by its output coil. Medical Systems. Circle 515.