Studies on neural circuits of posterior parietal cortex in multisensory perception and integration

Abstract

Mammalian brain constantly perceive multiple sensory information simultaneously and integrate them into one percept to make optimal behavior outputs. Depending on the congruency and salience of the modality-specific information, enhancement in perception or sensory dominance could appear as a result of multisensory integration. However, we still do not fully understand the underlying neural circuit mechanism. To identify this, we established two types of perceptual behavior paradigms under a simple go/no-go regime: visual-auditory modality discrimination task and visual-auditory information discrimination task. Using these paradigms, we found that the audition dominates the vision during audiovisual conflicts. Co-activation of visual (VC) and auditory (AC) cortices can induce the auditory dominance by suppressing visual-responsive neurons in the PPC, implying that interaction between the inputs from VC and AC in the PPC is important for mediating the auditory dominance. We further identified that among the sub-areas within the PPC, central PPC area (VISa

anterior visual area) receives similar amount of visual and auditory inputs, and its PV$^+$ interneurons mainly receive auditory inputs. Pharmacological inactivation of the PPC or optogenetic inactivation of its PV$^+$ interneurons weakened the auditory dominance by abolishing the auditory-to-visual feedforward inhibition via PV$^+$ interneurons in the PPC. On the contrary, optogenetic activation of PV$^+$ neurons in the PPC enhanced the auditory dominance. These data indicate that activation of PV$^+$ neurons in the PPC is necessary and sufficient for generating auditory dominant perceptual behaviors in mice resolving audiovisual conflicts. We further found that PPC activity is also necessary for integrating the congruent cross-modal information and enhancing the behavioral performance, but PV$^+$ neurons in the PPC were not responsible for the enhancement.We next observed the behavioral changes during the integration of multi-modal information using a mouse model of autism, which is a psychiatric disorder having problems in sensory processing. The mutant mice showed the weakening of auditory dominance and multisensory enhancement in the multisensory trials as shown in the mice with the PPC inactivation. We further identified that these mice showed the severe disruptions in the cortical inputs to the PPC, especially from the frontal and the auditory cortices. Collectively, our data demonstrate that a local circuit in the PPC is critical for the auditory dominance over vision in mice resolving cross-modal conflicts. Furthermore, we identified that this circuit is disrupted in the mouse model of autism.