SCALP TOPOGRAPHY AND ANALYSIS OF INTRACRANIAL SOURCES OF FACE-EVOKED POTENTIALS

Several reports have described that a positive vertex peak of an evoke d potential varied in amplitude and latency specifically when images o f faces were the eliciting stimulus. The scalp topography and the poss ible underlying dipole sources of this peak are the subject of this re port. We presented black-and-white photographs of human faces, flowers and leaves to 16 healthy subjects and recorded the evoked brain poten tials from 31 scalp electrodes. We found the previously described high er amplitude of the positive vertex peak when faces were the crucial s timulus, but the latency of this peak was the same (180 ms) for all th ree categories of stimulus. At the posterior temporal electrodes, the face waveforms showed a negative peak at 175 ms, which was only rudime ntary in the waveforms elicited by the other stimuli. Since in most pr evious reports a mastoid reference was used, it is most likely that th e previously described latency shift of the positive vertex peak assoc iated with face stimuli was due to the interaction with this posterior temporal peak. The dipole analysis of the possible generators of the recorded potentials suggested the sequential activation of occipital, lateral temporal and mesio-temporal brain structures during the percep tion of a human face.