A comparison of multisensory features of two auditory cortical areas: primary (A1) and higher-order dorsal zone (DZ)

Abstract

From myriads of ongoing stimuli, the brain creates a fused percept of the environment. This process, which culminates in perceptual binding, is presumed to occur through the operations of multisensory neurons that occur throughout the brain. However, because different brain areas receive different inputs and have different cytoarchitechtonics, it would be expected that local multisensory features would also vary across regions. The present study investigated that hypothesis using multiple single-unit recordings from anesthetized cats in response to controlled, electronically-generated separate and combined auditory, visual, and somatosensory stimulation. These results were used to compare the multisensory features of neurons in cat primary auditory cortex (A1) with those identified in the nearby higher-order auditory region, the Dorsal Zone (DZ). Both regions exhibited the same forms of multisensory neurons, albeit in different proportions. Multisensory neurons exhibiting excitatory or inhibitory properties occurred in similar proportions in both areas. Also, multisensory neurons in both areas expressed similar levels of multisensory integration. Because responses to auditory cues alone were so similar to those that included non-auditory stimuli, it is proposed that this effect represents a mechanism by which multisensory neurons subserve the process of perceptual binding.

Development of Multisensory Processing in Ferret Parietal Cortex.

“…Thus, the observed non-integrative effects could not have been induced by inhibitory effects of one stimulus being presented outside of its receptive field. Numerous reports have documented and examined non-integrated multisensory responses in bimodal neurons in a variety of neural areas (Perrault Jr et al , 2005;Meredith et al , 2021;Merrikhi et al , 2022a;Merrikhi et al , 2022b). The present study shows that such non-integrative multisensory effects were strongly influenced by development because, as depicted in Figure 5D, significant shifts were seen from primarily suppressive levels in infants to progressively higher levels of multisensory response change across the periods of adolescence.…”

“…We also examined the subthreshold form of multisensory neuron across the different age groups. Although small in occurrence (as also observed in other areas - (Meredith et al , 2021;Merrikhi et al , 2022a;Merrikhi et al , 2022b), their proportions showed an increasing trend during development but no developmental pattern for changes in MSI levels were demonstrated. A similarly low incidence of multisensory response depression revealed the presence of the effect during development, but consistent changes across development could not be assessed.…”

“…In addition, multisensory neurons can respond to multisensory stimulation without exhibiting MSI, but with responses that fail to achieve a statistically significant difference from their most effective unisensory response (e.g., see (Perrault Jr et al , 2005)). Such non-significant response changes, however, can contribute to substantial effects at the population level (Merrikhi et al , 2022a;Merrikhi et al , 2022b) although their developmental presentation is not known. Furthermore, the AES area is a conglomerate region consisting of 3 different sensory representations, each with their own connectional features and functional properties (for review, see (Meredith et al , 2018)).…”

Deafness induces complete crossmodal plasticity in a belt region of dorsal auditory cortex

“…However, the organisational patterns observed for sensory responses in hearing animals was not observed. Specifically, for hearing DZ, visual responses were segregated posteriorly in the structure, presumably near the sources of visual cortical inputs, whereas somatosensory responses were clustered anteriorly, near presumed sources of somatosensory cortical inputs (Merrikhi et al, 2022, 2023). In contrast, no distributional trends were observed for visual or somatosensory responses in the early‐deaf DZ that essentially filled the entire extent of the region.…”

“…Auditory response features of DZ include longer latency responses and broader frequency tuning than found in A1, as well as responses to complex auditory cues (He et al, 1997; Stecker et al, 2005). In addition, a large proportion (>76%) of DZ neurons exhibit visual and/or somatosensory influences that were differentially distributed in the region (Merrikhi et al, 2022, 2023). Furthermore, approximately 57% of neurons showed multisensory convergence, of which many demonstrated multisensory integration in response to multisensory stimulation.…”