Prefrontal cortex (PFC) and posterior parietal cortex are key brain areas for magnitude representations. Whether active discrimination of numerosity changes neuronal representations is still not known. We simultaneously recorded from the same recording sites in the PFC and ventral intraparietal area (VIP) before and after monkeys learned to actively discriminate the number of items in a set. Only PFC neurons, and not VIP neurons, exhibited heightened representation of number after numerosity training. Increased responsiveness of PFC was evidenced by enhanced differentiation of numerosity by the population of neurons, as well as increased numerosity encoding by individual selective neurons. None of these effects were observed in the VIP, in which neurons responded invariably to numerosity irrespective of behavioral relevance. This suggests elevated PFC participation during numerical task demands and executive control, whereas VIP encodes quantity as a perceptual category regardless of behavioral relevance.
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