P300: the similarities and differences in the scalp distribution of visual and auditory modality.
PURPOSE: To examine the topographic relationship of P3(00) between the visual and auditory modalities, especially to examine whether there are any modality-specific hemispheric differences of P3 in normal adults. METHODS: The P3s were recorded from the same 41 normal right-handed males between the ages of 20 and 33 in both a typical auditory oddball task and a visual oddball paradigm with novel stimuli, with an extensive set of 61 scalp electrodes. In addition to the visual comparison and quantitative assessment of current source density (CSD) maps between the two modalities, canonical correlation analyses on the P3 raw amplitudes and examination of interaction effects of modality x location on both raw and normalized P3 data were performed. RESULTS: The canonical correlation between modalities was generally high, especially at the left parietal brain region. There were no significant hemispheric effects in anterior brain but significant left-greater-than-right hemispheric effects in posterior brain regions in both modalities; modality-specific hemispheric effect was observed only at the parietal region. Strong surface current density activities were observed in the midline parietal-occipital area, and left and right boundary areas of temporal and inferior frontal region. CONCLUSIONS: The topographic similarities between P3s recorded in the visual and auditory modality outnumber the differences. Combining data from CSD assessments and profile analysis of P3 topography support the hypothesis of multiple generators of P3 that are differentially active in processing stimuli from different sensory modalities and are not symmetrically distributed between the two hemispheres.