Analysis of processing in somatosensory input by using MEG

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We investigated the cortical activation following two points tactile stimulation to tip of index finger of right hand and bilateral hands. We used a 306-ch whole-head MEG system and a tactile stimulator driven by piezoelectrical actuator. An array of two tiny plastic pins of the stimulator was used to obtain the somatosensory evoked magnetic fields (SEF). The distance between pins was set at 7.2mm that all subjects detect clearly for constant distance stimuli condition and at2.4mm, 4.8mm and 7.2mm for two points discrimination (2PD condition). In 2PD condition, three kinds of stimulation were given randomly. The stimulation to bilateral hand was given simultaneously. We confirmed three peaks of SEF waveforms around the somatosensory cortex in the left hemispheres in both conditions in unilateral and bilateral stimulations. There were no significant differences in the peak latencies in both conditions between unilateral and bilateral stimulations. The second and third peaks in 2Pcondition in bilateral stimulations increased in amplitude significantly. The ECDs corresponding to these peaks were located in posterior portion from area 3b.