Odor quality coding and categorization in human posterior piriform cortex

Abstract

This study reports that odorants that elicited similar fMRI activity patterns in the posterior piriform cortex were more likely to be judged as being more perceptually alike. This correlation between spatially distributed activity and perceptual judgments was not reproduced in other areas of the brain, suggesting that the posterior piriform cortex contains a spatially distributed ensemble code for odor object quality. Efficient recognition of odorous objects universally shapes animal behavior and is crucial for survival. To distinguish kin from nonkin, mate from nonmate and food from nonfood, organisms must be able to create meaningful perceptual representations of odor qualities and categories. It is currently unknown where and in what form the brain encodes information about odor quality. By combining functional magnetic resonance imaging (fMRI) with multivariate (pattern-based) techniques, we found that spatially distributed ensemble activity in human posterior piriform cortex (PPC) coincides with perceptual ratings of odor quality, such that odorants with more (or less) similar fMRI patterns were perceived as more (or less) alike. We did not observe these effects in anterior piriform cortex, amygdala or orbitofrontal cortex, indicating that ensemble coding of odor categorical perception is regionally specific for PPC. These findings substantiate theoretical models emphasizing the importance of distributed piriform templates for the perceptual reconstruction of odor object quality.