Auditory-to-visual feedforward inhibition mediates auditory dominance during the integration of audiovisual conflict
Conflicts between the sensory modalities by humans, and the brain resolves these conflicts through the fast integration to elicit coherent perceptual behavior. During the integration of audiovisual conflict, one modality often dominates over the other, but the underlying neural mechanism remains unclear. We recently found that the direct inputs from primary visual (VC) and auditory (AC) cortices to the posterior parietal cortex (PTLp) are critical for mediating auditory dominance over vision. Parvalbumin-positive (PV+) interneurons in the PTLp receive strong inputs from AC, and optogenetic inhibition of these neurons abolishes auditory dominance without affecting either sensory perception. Consistent with this behavioral result, we found that optogenetic inhibition of PV+ interneurons relieved the suppression on visual-selective neurons by auditory inputs. Thus, we concluded that this ‘auditory-to-visual feedforward inhibition’ is mediated by PV+ interneurons in the PTLp and leads to auditory dominance during the integration of audiovisual conflict. These recent results, acquired by KAIST researchers in the Department of Biological Sciences, were published in Neuron
Visual and auditory stimuli can exhibit sufficient mismatches and generate cognitive conflicts; in this case one sensory modality often predominates over the other in the resolution of a conflict. It can improve perceptual performance in response to sensory conflicts and help animals make fast and accurate decisions in a complex, ambiguous environment. However, the neural basis for perceptual dominance during the integration of the conflict between sensory modalities it is not yet fully understood. Recent published results by researchers at KAIST have involved the identification of neural circuits for auditory dominance over vision by using behavioral, anatomical and physiological methods.
First, the visual-auditory discrimination tasks were devised, in which head-fixed mice were trained to discriminate visual and auditory information under a go/no-go regime. We found that mice showed auditory-dominant perceptual behaviors in resolution to audiovisual conflicts.
Second, retrograde tracing of PTLp neurons were performed by injecting retrobeads and anterograde tracing of VC and AC neurons by injecting adeno-associated viruses. The researchers anatomically identified the converging inputs to the PTLp from VC and AC. They further dissected the synaptic inputs to different types of PTLp neurons by using the pseudo-typed rabies virus. Interestingly, unlike excitatory neurons receiving similar amount of inputs from VC and AC, parvalbumin-positive (PV+) interneurons in the PTLp receive biased inputs from AC, i.e. stronger inputs from AC than VC.
Third, consistent with the behavioral and anatomical findings, it was found that only VC-selective neurons in the PTLp showed significant reduction in their firing activity upon receiving both VC and AC inputs. Furthermore, this AC-induced suppression of VC-selective neurons in the PTLp was relieved when PV+ interneurons were optogenetically inhibited.
Finally, validation was obtained regarding the function of the PV+ inhibitory circuit in the PTLp. When the PTLp was inactivated by injecting muscimol or optogenetically inhibited its PV+ interneurons in mice perceiving audiovisual conflicts, the auditory dominance was abolished while either visual or auditory perception was intact.
In summary, the researchers identified AC input-specific feedforward inhibition of VC inputs converging on the PTLp, which led to auditory dominance during the cross-modal resolution of conflicts. Here, PV+ interneurons in the PTLp play a crucial role in this feedforward inhibition. These findings by KAIST researchers provide critical insights into the circuit mechanism of cross-modal interaction in the mammalian cortex.
By You-Hyang Song, Jae-Hyun Kim and Seung-Hee Lee, Department of Biological Sciences
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