Matt Smear

From MainenLab

The “where” problem of olfaction: behavioral strategies and neural mechanisms

Neuroscience can be performed at the molecular, cellular, systems, and behavioral levels. In what animal can we best test hypotheses about how to unify these levels? Ideally, that animal would combine fly genetics with primate psychophysics and electrophysiology. Evolution is unlikely to accommodate us any time soon, so we need a compromise candidate - perhaps the best is the rodent, mouse or rat. Genetic manipulations cannot yet be targeted in a rodent with the specificity and ease obtainable in worms and flies, but rodent transgenesis is becoming increasingly powerful, as are the genetically-encoded indicators and perturbers of function. These genetic tools can be complemented with electrophysiological methods that permit real-time recording of many well-isolated neurons in freely-moving rodents. So while the rodent approaches our ideal in terms of amenability to genetics and electrophysiology, its repertoire of behaviors amenable to psychophysics is impoverished, especially compared to that of the primate.

So, what behavioral problem should we study in the rodent? Olfaction seems to be the rodent’s best sense, which favors the idea that they possess fascinating olfactory behavioral strategies to which their brains devote sophisticated neural mechanisms. While our understanding of odor identification, the “what” problem of olfaction, has progressed, the “where” problem of olfaction has received relatively scant attention. Yet, arguably at least, locating an odor source matters just as much as identifying it: distinguishing a meal from a predator is futile if you avoid the former or approach the latter. Our present goal is to make the rodent’s “where” problem of olfaction tractable to psychophysical techniques. We have designed an olfactorium in which rats navigate to odor sources. For odor stimuli delivered to the olfactorium, we can characterize spatiotemporal odor concentration patterns with high spatial, temporal, and concentration-level resolution. In addition, we can precisely track the nose position of a freely-moving rat at video-rate time resolution in real time. By combining odor concentration measurements with tracked trajectories, we hope to reconstruct the time-varying odor concentration pattern experienced by a navigating rat, and thereby reverse engineer its navigation strategies. In the future, we intend to exploit rodent neuroscience’s growing arsenal of tools for electrophysiology and transgenesis in the context of olfactospatial psychophysics, in order to understand the neural circuitry of olfactory “where”.

An animation of a rat making exploratory head movements as it seeks an odor source:

EMAILS: M A T T dot C S H L at G M A I L

My cv: Matt Smear's CV‎

I was trained at UCSF, in Herwig Baier's lab.

My fiance & I, posing in front of 2 Sol Lewitt eyesores:

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