…and why, to most of us, do lemon and pizza smell different? And, given this invariance, why is smell such a personal, individualized sense? Stan Pashkovski recently published a gorgeous paper (here) addressing these fundamental questions in olfactory biology. Answering these questions, in the end, comes down to understanding how information about odor chemistry – the stimulus feature that the olfactory system cares about – is organized in cortex, how that organization might be invariant across individuals, and how that organization is made plastic based upon context and an individual’s experience. Surprisingly, though, to date no one had identified systematic representations for odor chemistry or odor chemical relationships in olfactory cortex (think about where systems neurobiology would be today if we didn’t at least have some understanding of this already for vision and audition!). To take on this longstanding challenge, Stan (with help from Giuliano and David) used an incredibly clever combination of chemoinformatics, multiphoton imaging and molecular/circuit manipulations to not only identify how cortex encodes chemical relationships, but to understand how cortex transforms information about relationships inherited from the sensory periphery based upon experience. The paper both articulates models for odor perception and argues that the olfactory cortex will be a perfect substrate for studying unsupervised learning…an ongoing scientific obsession in the lab. A huge congrats to Stan on this tour-de-force!