Rapid, Experience-Induced Enhancement in Odorant Discrimination by Anterior Piriform Cortex Neurons

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Abstract
Current views of odorant discrimination by the mammalian olfactory system suggest that the piriform cortex serves as a site of odor object synthesis. Given the enormous number of odorant feature combinations possible in nature, however, it seems unlikely that cortical synthetic receptive fields (RFs) are innate but rather require experience for their formation. The present experiment addressed two issues. First, we made a direct comparison of mitral/tufted cell and anterior piriform cortex (aPCX) neuron abilities to discriminate odorant mixtures from their components to further test whether aPCX neurons can treat collections of features different from the features themselves (synthetic coding). Second, we attempted to determine the minimum duration of experience necessary for formation of cortical synthetic RFs. Single-unit recordings were made from mitral/tufted cells and aPCX layer II/III neurons in urethan-anesthetized rats. Cross-habituation between novel binary mixtures and their novel components was used to determine odor discrimination abilities. The results suggest that after ≥50 s of experience with a binary mixture, aPCX neurons can discriminate the mixture from its components, whereas mitral/tufted cells cannot. However, when limited to 10 s of experience with the mixture, aPCX neurons appear similar to mitral/tufted cells and do not discriminate mixtures from components. These results suggest experience-dependent synthetic processing in aPCX and suggest an important role for perceptual learning in normal odor discrimination.