Striate Cortical Generators of the N75, P100 and N145 Components Localized by Pattern Reversal Visual Evoked Magnetic Fields

Magnetic fields evoked by checkerboard pattern reversal visual stimulation to the monocular left or right half-field were recorded over the whole head using a helmet-shaped 64 channel magnetoencephalography system in fourteen normal subjects. The sources of the triphasic N75m-P100m-N145m responses were located using a single current dipole model. Relative locations and orientations of the N75m and N145m dipoles to the P100m dipole were calculated for each subject to reduce errors due to anatomical variability and then averaged for all subjects under the same stimulus conditions. These averaged parameters showed that N75m and N145m originated from the same location in the striate cortex as P100m and reversed their orientations successively by 180° during the time course.