Somatosensory evoked magnetic fields after mechanical stimulation of the scalp in humans

Somatosensory evoked magnetic fields after mechanical stimulation by air-pressure-induced tapping which was applied to the forehead and occiput were examined in normal human subjects. The equivalent current dipole (ECD) of the initial magnetic field, 1M, was identified in the primary somatosensory cortex (SI) in the hemisphere contralateral to the stimulation. The ECD of the subsequent magnetic fields, 2M, was identified in bilateral second sensory cortices (SII). The ECD position of 1M in SI generated after the scalp stimulation was closely inferior to the hand area of the SI, which was consistent with the well-known somatotopic organization, 'homunculus'.