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Abstract

The world we live in abounds with sensory stimuli. These rarely occur in one sensory modality alone. Therefore,
brain function depends on proper integration and segregation of multiple cues in order to master processing a
complex scenery. To perform this task, neural activity evoked by separate modalities has to be integrated across
space and time. Previous reports indicate that intermodal areas, that are localized between primary sensory areas,
may play an important role in this process1. One advantage of such intermodal cortical fields is that not all afferent
activity needs to be routed via long range connections and thalamic input, but instead, propagating network
activity from proximal primary modalities can directly influence local circuit function2. We used intrinsic optical
imaging and electrophysiological methods to investigate the spatiotemporal properties of multisensory integration
in such an intermodal cortical area. First, we mapped the neurovascular response of rat neocortex in response to
light flashes and whisker deflection, and indentified unisensory and multisensory areas. In the same animals, we
inserted laminar electrodes to record local field potentials, current source densities and multiunit activity within this optically identified multisensory cortical field. Our results suggest that multimodal integration in these intermodal cortical fields relies primarily on sublinear processes, with multisensory response being less than the sum of unisensory responses. These findings support previous studies which question a predominant role of superadditivity for multisensory integration in the cortex.