Categorization is a fundamental cognitive process by which we classify and rapidly generalize learned and novel information. But how are category-defining associations represented in the brain? Using a new paradigm for studying category learning in mice, we investigated how the representation of a learned category in the mouse prefrontal cortex emerges over time. In a subsequent study, we traced the effects of category learning back to higher visual area POR and identified a possible mechanism by which sensory neurons can acquire category selectivity. The identification of neuronal circuits and computations underlying learned categorization in mice can ultimately provide new insights into the basic implementation of associative memory in the brain.