What is a multisensory cortex? A laminar, connectional, and functional study of a ferret temporal cortical multisensory area

Now that examples of multisensory neurons have been observed across the neocortex, this has led to some confusion about the features that actually designate a region as “multisensory.” While the documentation of multisensory effects within many different cortical areas is clear, often little information is available about their proportions or net functional effects. To assess the compositional and functional features that contribute to the multisensory nature of a region, the present investigation used multichannel neuronal recording and tract tracing methods to examine the ferret temporal region: the lateral rostral suprasylvian sulcal area. Here, auditory‐tactile multisensory neurons were predominant and constituted the majority of neurons across all cortical layers whose responses dominated the net spiking activity of the area. These results were then compared with a literature review of cortical multisensory data and were found to closely resemble multisensory features of other, higher‐order sensory areas. Collectively, these observations argue that multisensory processing presents itself in hierarchical and area‐specific ways, from regions that exhibit few multisensory features to those whose composition and processes are dominated by multisensory activity. It seems logical that the former exhibit some multisensory features (among many others), while the latter are legitimately designated as “multisensory.” Multisensory processing occurs across the neocortex, but what makes an area multisensory? Multisensory processing in ferret lateral rostral suprasylvian (LRSS) area was examined using tract tracing and multichannel neuronal recording and compared with other cortical areas. Inputs from lower level auditory and somatosensory cortices converged in the LRSS, where the majority of neurons were auditory‐somatosensory multisensory and multisensory activity was the dominant output signal. Comparison with similarly studied cortical areas indicates that areas dominated by multisensory activity are appropriately designated as multisensory.