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Abstract

Responses to crossmodal stimuli have been observed in a wide range of brain regions, where they have been studied in great detail. Although many crossmodal areas have been characterized, the spatiotemporal characteristics of such activity are still largely unknown. We used voltage-sensitive dye imaging (VSDI) to address this question. For the presented study, three cortical regions in rat were imaged: primary
visual cortex (V1), barrel field of primary somatosensory cortex (S1bf) and parietal
association area (PA, flanked by V1 and S1bf). We find that sensory-evoked
population activity can propagate in the form of a distinct wave, robustly in either
crossmodal direction, i.e. from S1bf to V1, or from V1 to S1bf. In single trials, the
waveforms changed continuously during propagation, with dynamic variability from
trial to trial, which we interpret as evidence for cortical involvement in the spreading
process. We further investigated the propagation of spontaneous sleep-like waves in this area using a novel flow-detection algorithm. Results of these experiments show that spontaneous activity also tends to propagate parallel to the crossmodal axis, rather than orthogonal to it. Taken together, these findings demonstrate that cortical networks can show pre-attentive crossmodal propagation of activity, and suggest a potential mechanism for the establishment of crossmodal integration.