Deactivation of Association Cortices Disrupted the Congruence of Visual and Auditory Receptive Fields in Superior Colliculus Neurons

Auditory-induced response in the primary sensory cortex of rodents

The details of auditory response at the subthreshold level in the rodent primary somatosensory cortex, the barrel cortex, have not been studied extensively, although several phenomenological reports have been published. Multisensory features may act as neuronal representations of links between inputs from one sensory modality to other sensory modalities. Here, we examined the basic multisensory postsynaptic responses in the rodent barrel cortex using in vivo whole-cell recordings of neurons. We observed robust responses to acoustic stimuli in most barrel cortex neurons. Acoustically evoked responses were mediated by hearing and reached approximately 60% of the postsynaptic response amplitude elicited by strong somatosensory stimuli. Compared to tactile stimuli, auditory stimuli evoked postsynaptic potentials with a longer latency and longer duration. Specifically, auditory stimuli in barrel cortex neurons appeared to trigger "up states", episodes associated with membrane depolarization and increased synaptic activity. Taken together, our data suggest that barrel cortex neurons have multisensory properties, with distinct synaptic mechanisms underlying tactile and non-tactile responses.

Spatial receptive field shift by preceding cross-modal stimulation in the cat superior colliculus

KEY POINTS

It has been known for some time that sensory information of one type can bias the spatial perception of another modality. However, there is a lack of evidence of this occurring in individual neurons. In the present study, we found that the spatial receptive field of superior colliculus multisensory neurons could be dynamically shifted by a preceding stimulus in a different modality. The extent to which the receptive field shifted was dependent on both temporal and spatial gaps between the preceding and following stimuli, as well as the salience of the preceding stimulus. This result provides a neural mechanism that could underlie the process of cross-modal spatial calibration.

ABSTRACT

Psychophysical studies have shown that the different senses can be spatially entrained by each other. This can be observed in certain phenomena, such as ventriloquism, in which a visual stimulus can attract the perceived location of a spatially discordant sound. However, the neural mechanism underlying this cross-modal spatial recalibration has remained unclear, as has whether it takes place dynamically. We explored these issues in multisensory neurons of the cat superior colliculus (SC), a midbrain structure that involves both cross-modal and sensorimotor integration. Sequential cross-modal stimulation showed that the preceding stimulus can shift the receptive field (RF) of the lagging response. This cross-modal spatial calibration took place in both auditory and visual RFs, although auditory RFs shifted slightly more. By contrast, if a preceding stimulus was from the same modality, it failed to induce a similarly substantial RF shift. The extent of the RF shift was dependent on both temporal and spatial gaps between the preceding and following stimuli, as well as the salience of the preceding stimulus. A narrow time gap and high stimulus salience were able to induce larger RF shifts. In addition, when both visual and auditory stimuli were presented simultaneously, a substantial RF shift toward the location-fixed stimulus was also induced. These results, taken together, reveal an online cross-modal process and reflect the details of the organization of SC inter-sensory spatial calibration.