THE EARLY COMPONENT OF THE VISUAL-EVOKED MAGNETIC-FIELD

SEVERAL EEG studies have reported an early component of the visual evo ked potential. However, it is controversial whether this component is cortical or subcortical. Our study has aimed to clarify this problem u sing MEG and EEG in nine normal volunteers. A total of 4000 stimuli we re presented to the monocular visual hemifield through a light-proof s timulating goggle and the visual evoked magnetic field and visual evok ed potential was measured above the occipital lobe. The early componen t was observed in three of the nine subjects. The latency ranged from 40 to 45 ms in MEG and from 39 to 47 ms in EEG. The result of dipole l ocalization analysis showed that its origin was cortical, and specific ally, the striate cortex.