Project Summary (Project 3: Representation of perceived odor intensity) The odor of French fries contains more than 500 molecules, but can be replicated by combining only 21 of them. The key to understanding which molecules matter and which are irrelevant is odor intensity. When odors are used to convey information, whether it be the ripeness of a fruit, the note of a predator, or the aroma of a potential mate, intensity is required to know how much is present and where to locate the source. Several neural models have been proposed to explain how the brain represents intensity, but most experimental manipulations manipulate intensity indirectly, by changing odor concentration, rather than directly delivering stimuli at a targeted perceived intensity. In this proposal we use human and mouse behavior to measure the perceived intensity of odors, and then use intensity-balanced odors to probe the neural correlates of perception. With access to the perceptual readout in a model system, we can also use genetic manipulations and optogenetic stimulation to probe how receptor activation profiles translate into perceived intensity. By examining both neural and perceptual responses to the same stimuli across both species, these experiments will reveal how intensity is encoded by receptor activation patterns, the bulb, and the cortex and develop models that predict perceived intensity based on either chemical structure or neural activity patterns.