Title: Ipsilateral primary sensorimotor cortical response to mechanical tactile stimuli Running head: iSMI response to mechanical stimuli

We studied somatosensory evoked fields elicited by mechanical vs. electrical stimuli to index finger of healthy subjects. Mechanical stimulation was index pulp compression and decompression by using non-magnetic 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 (cSI) responses in all respective subjects. Compressive-stimuli evoked ipsilateral primary sensorimotor cortical responses in all respective subjects, with dipole strengths less than cSI 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 to electrical stimulation.