The Neural Basis of Quantity Discrimination in Mice

Quantity discrimination is an ability of identifying preferable sizes or amounts of subjects, yet its 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, disrupts this behavior. Two-photon analysis reveals that selected neurons with preferential activities or Number Neurons are detected at a given time; however, these neurons are not correlated with quantity discrimination behavior and alter their preferential identities over time. Furthermore, inhibition of other cortex regions with Number Neurons does not affect quantity discrimination. Conversely, the PPC neuronal population changes synchronous firing levels, which correlates with quantity discrimination behavior and could be explained by a Neural Entropy model. Together, our study identifies a central role of the PPC in quantity discrimination, providing a neuronal population model of synchronous firing for quantity discrimination coding.