Ipsilateral primary sensorimotor cortical response to mechanical tactile stimuli.

We studied somatosensory-evoked fields elicited by mechanical versus electrical stimuli to index finger of healthy participants. Mechanical stimulation was index pulp compression and decompression by using nonmagnetic mechanical stimulator. Electrical stimulation was three times of sensory threshold and delivered to index pulp by using ball-shaped electrodes. Mechanical/electrical stimuli evoked contralateral primary somatosensory cortical responses in all respective participants. Compressive stimuli evoked ipsilateral primary sensorimotor cortical responses in all respective participants, with dipole strengths less than contralateral primary somatosensory cortical responses of compressive stimuli. Mechanical/electrical stimuli evoked secondary somatosensory (SII) cortical responses bilaterally; electrical-stimuli SII dipole strengths were relatively stronger than compressive-stimuli SII responses. It is concluded that the use of mechanical stimulation may improve our understanding of functional sensory cortical responses compared with electrical stimulation.