TEMPORAL PRECISION AND DYNAMICAL CODING IN THE OLFACTORY BULB

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Identification of the stimulus features represented by neuronal activity, and understanding the fidelity of this representation, are central to understanding how the brain processes the sensory world. In the mammalian olfactory bulb, mitral/tufted (M/T) cells both receive synaptic input from sensory neurons, and serve as the principal output to central brain structures. Due to physical constraints, odor intensity (concentration) at odorant receptors in vertebrates is likely to vary much more slowly than stimulus intensity in other sensory modalities such as vision or audition. Because of this speed limit, the precise timing of action potentials (APs) will not track rapid, millisecond-timescale changes in stimulus properties as in other sensory systems. Rather, the extra "bandwidth" afforded by precise AP timing could encode other olfactory stimulus features, such as identity or context. If odor identity is encoded in AP timing early during a stimulus response, and this timing is reliable across identical stimuli, behavioral response latencies could be minimized11. Across respiratory cycles, an identical ensemble AP response could serve to confirm odor identity. Alternatively, directed changes in this response across cycles could convey novel information in each respiratory cycle about a complex stimulus. Here I propose to test the hypotheses that ensemble AP timing encodes features of odor stimuli in the mouse olfactory bulb, and does so in a dynamic fashion across respiratory cycles.