Population coding of quantity discrimination in mouse posterior parietal cortex

Quantity discrimination, the ability to identify preferable sizes or amounts of objects, is well-documented across humans and animals, yet its underlying neural mechanisms remain elusive. Here, we report that mice exhibit an innate quantity discrimination behavior for food amounts, consistent with the Weber-Fechner law. Inhibition of the Posterior Parietal Cortex (PPC), but not other cortex regions, abolishes this behavior. Two-photon calcium imaging reveals that the PPC neurons with preferential activities towards food amounts are detected at a given time; however, their preferential identities change over time. Conversely, the PPC exhibits population synchrony during quantity discrimination, and the levels of population synchrony correlate with food amounts. Together, our study identifies a central role of the PPC in quantity discrimination, providing a population coding for quantity discrimination.