The olfactory system is a unique and powerful model for addressing how genetically-defined inputs to the brain contribute to stimulus perception. Nowhere in the mammalian nervous system is there a more direct relationship between single genes and sensory inputs. The response profile of each olfactory sensory neuron is determined by a single expressed olfactory receptor gene. The receptor directs axon guidance, so that axons from sensory neurons that express the same receptor converge to form spherical structures called glomeruli. Thus, the first representation of olfactory information, the map of glomeruli in the olfactory bulb, is highly amenable to genetic manipulation. Using behavioral techniques in genetically modified mice, we are currently exploring two fundamental questions related to olfactory perception:

• What is the contribution of individual receptors to odor perception?
• How does glomerular organization influence odor perception?

Olfactory bulb output neurons (mitral and tufted cells) receive exclusive input from a single glomerulus, and project broadly to all nine regions of the olfactory cortex. Thus, sensory input is relayed to multiple brain regions simultaneously. Using a combination of optogenetic and optical imaging techniques, we are currently exploring two fundamental questions related to higher order olfactory processing:

• What is the contribution of individual olfactory cortical regions to odor perception?
• How does glomerular identity and location influence odor coding in the olfactory cortex?