Dipole orientation differs between high frequency oscillations and N20m current sources in human somatosensory evoked magnetic fields to median nervestimulation

The dipole orientation of equivalent current source for the high frequency oscillations (HFOs) above 300 Hz and that for the underlying N20m were comp ared. Somatic magnetic fields were recorded over the left hand somatosensor y area to right median nerve stimulation at the wrist with a wide-bandpass (0.1-2000 Hz). The HFOs and underlying N20m were extracted by digital filte ring of 300-900 Hz and 1-300 Hz, respectively. We found that the orientatio n of the HFOs and underlying N20m current sources differs and that the HFO source orientation shows a more divergent pattern than the N20m. These resu lts suggest that the somatosensory HFOs are not generated from the pyramida l cell population in area 3b which produces the underlying N20m and that th ey may reflect activities of the non-pyramidal neuron population. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.