Multisensory auditory-somatosensory interactions in early cortical processing revealed by high-density electrical mapping

We investigated the time-course and scalp topography of multisensory intera ctions between simultaneous auditory and somatosensory stimulation in human s. Event-related potentials (ERPs) were recorded from 64 scalp electrodes w hile subjects were presented with auditory-alone stimulation (1000-Hz tones ), somatosensory-alone stimulation (median nerve electrical pulses), and si multaneous auditory-somatosensory (AS) combined stimulation. Interaction ef fects were assessed by comparing the responses to combined stimulation with the algebraic sum of responses to the constituent auditory and somatosenso ry stimuli when they were presented alone. Spatiotemporal analysis of ERPs and scalp current density (SCD) topographies revealed AS interaction over t he central/postcentral scalp which onset at approximately 50 ms post-stimul us presentation. Both the topography and timing of these interactions are c onsistent with multisensory integration early in the cortical processing hi erarchy, in brain regions traditionally held to be unisensory. (C) 2000 Els evier Science B.V. All rights reserved.