Development of multisensory processing in ferret parietal cortex

It is well known that the nervous system adjusts itself to its environment during development. Although a great deal of effort has been directed towards understanding the developmental processes of the individual sensory systems (e.g., vision, hearing, etc.), only one major study has examined the maturation of multisensory processing in cortical neurons. Therefore, the present investigation sought to evaluate multisensory development in a different cortical region and species. Using multiple single‐unit recordings in anaesthetised ferrets (n = 18) of different ages (from postnatal day 80 to 300), we studied the responses of neurons from the rostral posterior parietal (PPr) area to presentations of visual, tactile and combined visual‐tactile stimulation. The results showed that multisensory neurons were infrequent at the youngest ages (pre‐pubertal) and progressively increased through the later ages. Significant response changes that result from multisensory stimulation (defined as multisensory integration [MSI]) were observed in post‐pubertal adolescent animals, and the magnitude of these integrated responses also increased across this age group. Furthermore, non‐significant multisensory response changes were progressively increased in adolescent animals. Collectively, at the population level, MSI was observed to shift from primarily suppressive levels in infants to increasingly higher levels in later stages. These data indicate that, like the unisensory systems from which it is derived, multisensory processing shows developmental changes whose specific time course may be regionally and species‐dependent. Multisensory (MS) integration can be observed when the combination of inputs from two or more unisensory modalities (i.e., visual and tactile) leads to statistically significant enhancement or suppression of neuronal firing in multimodal neurons. Multisensory (MS) enhancement is usually linked to processes that increase perception (i.e., lip reading), whereas MS suppression is often associated with filtering unwanted information. Using in vivo electrophysiology in ferrets, we showed that the proportion of neurons exhibiting MS enhancement gradually increased from infancy to late adolescence. Moreover, MS suppression showed an opposite developmental trend, with more neurons suppressing during infancy and this proportion reducing gradually until late adolescence. These findings suggest that developmental changes in MS integration may contribute to changes i