Source of somatosensory primary cortical evoked magnetic fields (N20m) elicited by index finger stimulation moves toward mediolateral direction in area 3b in man.

摘要

In the present study, we analyzed the equivalent current dipole (ECD) movement around the peak of N20m primary cortical response elicited by the index finger stimulation. Somatosensory evoked magnetic fields by means of averaging 10000 epochs were recorded over the hand area contralateral to the stimulation side. In eight of 11 subjects, localization of an ECD for N20m was successively calculated for periods of 2.4 ms around N20m peak with a good accuracy (goodness-of-fit >0.95, correlation >0.95). The mean signal-to-noise ratio of 46.8 was sufficient to assess the ECD movement of approximately 1 mm. The ECD moved toward the anterior, lateral and inferior direction and mean excursion of ECD was 8.4 mm. This direction and the distance of N20m ECD movement in the present study were very similar to those by median nerve stimulation at the wrist (Neurosci. Lett. 280 (2000) 25). These results suggest that the distance of N20m ECD movement is independent of the size of projected area and reflect a sequential activation of the pyramidal cells in the somatosensory cortex mediated by horizontal connections running parallel to the cortical surface.