Brain electrical and magnetic fields from verbal cognitive activities evoked by a visual task

This study focuses on the investigation of higher brain function using electroencephalogram (EEG) and magnetoencephalogram (MEG) techniques. The authors observed verbal cognitive activities by measuring EEGs and MEGs evoked by visually cognitive tasks. English words, meaningless sets of letters, and simple flashes were presented. The authors analyzed the EEG and MEG data with a subtraction technique and topographic maps. Visual evoked potentials (VEPs) associated with cognition of meanings were obtained by subtracting VEPs evoked by random letters from VEPs evoked by English words. The topographic EEG maps in several subjects show a clear interhemispheric difference between latencies of 300 and 600 msec. The EEG maps in a few subjects, however, show no interhemispheric differences