Reduced activity of parvalbumin-positive interneurons in the posterior parietal cortex causes visually dominant multisensory decisions in freely navigating mice.

Multisensory integration is vital for animals to make optimal decisions in a complicated sensory environment. However, the neural mechanisms for flexible multisensory behaviors are not well understood. Here, we found that mice exhibit auditory-dominant decisions in the head-fixed and stationary state and switch to make visual-dominant decisions in the freely navigating state to resolve audiovisual conflicts. To understand the neural mechanism of the state-dependent switch in multisensory decisions, we performed in vivo calcium imaging of parvalbumin-expressing (PV) inhibitory neurons in the posterior parietal cortex (PPC), which are known to mediate auditory dominance in the resolution of audiovisual conflicts, in mice on the treadmill. In the stationary state, the PPC PV neurons showed similar amounts of evoked activity in responses to auditory and visual stimuli and enhanced responses to the multisensory audiovisual stimuli. Conversely, when mice were running on a treadmill, the PV neurons lost auditory responses and did not show any multisensory enhancement in their activity. When we optogenetically activated the PPC PV neurons in mice freely navigating the T-maze, the mice made more auditory-dominant decisions without changes in unisensory decisions. Our data demonstrate that the PPC PV neurons lost their ability to integrate auditory information with the visual one during active navigation. This modulation of the PPC PV neuron activity is critical for animals to make adaptive multisensory decisions according to their behavioral states.