Project Summary As the largest cortical recipient of direct olfactory bulb (OB) projections and a prominent part of the rodent brain, the piriform cortex (PCx) is considered to be a central hub for the processing and coding of olfactory information. While landmark studies have made significant progress towards deciphering PCx odor coding, there remains (in many cases) a significant disconnect between our understanding of olfactory perception and the coding principles that underlie it. For example, the PCx exhibits a massive over-representation of identity information that appears disproportional to the number of glomerular inputs necessary to encode odor features or drive odor-guided behavior. The efficient coding hypothesis predicts that in a low-noise situation (i.e., one with sparse receptor activation), the neuronal population should remove redundancies in order to most efficiently encode the stimulus. In a high noise situation (i.e., one with significant non-target receptor activation), the system should attempt to encode the stimulus in the most robust manner possible, by becoming highly redundant. Thus far, the stimulus concentrations utilized to examine PCx neural activity are typically many orders of magnitude above natural odorant concentrations - potentially signifying that these coding principles have been examined primarily in high neural noise situations. The ability to examine PCx neural activity within sparse receptor activation regimes will ultimately require knowledge about the limits of perceptual sensitivity and necessitate analyzing odor-evoked responses at both single neuron and ensemble levels. Here, we propose a technically innovative approach that will refine the current model of PCx odor coding. Specific Aim 1 will examine how the neural dynamics of individual and ensemble PCx neurons encode odor identity across different concentration regimes by utilizing high density recording across eight PCx locations, spanning a total A-P distance of 2.7mm. Specific Aim 2 will utilize the same electrophysiological approach in conjunction with our robust behavioral measures of sensitivity to investigate how the coding principles identified in Aim 1 predict perceptual ability. Achieving these aims will offer a unique and unparalleled window into odor processing by analyzing PCx neural activity at both local and mesoscale levels, across different concentration regimes, in a manner that can be correlated to perception.