FRONTO-PARIETAL CORTICAL INTERACTIONS FOR MULTISENSORY DECISIONS

The fronto-parietal network in the mouse neocortex is an important hub for evidence accumulation, transforming sensory inputs into decisions and actions. How the brain learns to combine evidence from different sensory modalities to instruct complex decisions remains poorly understood. Layer 5 pyramidal neurons (L5 Pyr) in posterior parietal cortex (PPC) are well positioned to integrate auditory and visual signals with inputs from frontal areas, specifically from anterior cingulate and secondary motor cortices (ACC/M2). Yet the principles and mechanisms of this integration and the functional relevance of fronto-parietal interactions are unknown. Here, we combine dual-color multi-compartment two‑photon calcium imaging and a multisensory decision-making task to dissect how axons from frontal regions and L5 Pyr in PPC encode auditory and visual information to guide behavioural choices. First, we quantified the neuronal fractions responding selectively to either visual or auditory stimuli or to both modalities under passive conditions, revealing diverse modes of audio-visual integration. Next, we simultaneously recorded activity in L5 Pyr and frontal axons during a multisensory decision-making task to determine whether frontal inputs gate PPC activity in a sensory‑modality‑specific fashion, biasing how auditory versus visual information are weighed during behavioural choices. Finally, we monitored the activity of frontal axons and PPC L5 Pyr neurons throughout task training to gain insight into learning-related adaptations. Together, these experiments will reveal the cellular and network‑level mechanisms by which fronto-parietal interactions help to integrate evidence across sensory modalities and utilize multi-modal information to guide choices.