Common basal extrastriate areas for the semantic processing of words and pictures

Objective: The recognition potential (RP) is an electrophysiological brain response which is sensitive to the semantic processing of meaningful stimuli. In this study we attempt to elucidate the topography and neural origin of the RP evoked by pictures and to compare it with the RP evoked by words. Methods: Words, pictures, Chinese characters and control stimuli were presented to 20 subjects following the rapid stream stimulation procedure. The activity was recorded using 60 cephalic electrodes. Results: We found a RP displaying its maximal amplitude at the left inferior parieto-occipital electrode (PO7) for words and at the right homologue electrode (PO8) for pictures and Chinese characters. Both the amplitude and the latency of the RP were larger in the case of words. A profile analysis indicated that the neural generators of the RP were common regardless of the type of stimulus, and a dipole analysis placed them about the lingual gyrus. Conclusions: Words and pictures share the same neural generators for the RP despite of subtle differences in lateralization. This is interpreted as an index of a multimodal semantic processing in basal extrastriate areas.