Nonsensory target-dependent organization of piriform cortex

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 111; no. 47; pp. 16931 - 16936
• Main Authors: Chen, Chien-Fu F., Zou, Dong-Jing, Altomare, Clara G., Xu, Lu, Greer, Charles A., Firestein, Stuart J.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 25.11.2014; National Acad Sciences
• Subjects: Animals; Axons; Biological Sciences; Brain; Injection sites; Mice; Neurons; Neuroscience; Odors; Olfactory bulb; Olfactory pathways; Olfactory perception; Pattern recognition; Piriform Cortex - anatomy & histology; Piriform Cortex - cytology; Pyramidal cells; Receptors; Recognition; Sensory perception; Sensory Receptor Cells - cytology; Topography; piriform cortex; olfaction; olfactory perception
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1411266111

The piriform cortex (PCX) is the largest component of the olfactory cortex and is hypothesized to be the locus of odor object formation. The distributed odorant representation found in PCX contrasts sharply with the topographical representation seen in other primary sensory cortices, making it difficult to test this view. Recent work in PCX has focused on functional characteristics of these distributed afferent and association fiber systems. However, information regarding the efferent projections of PCX and how those may be involved in odor representation and object recognition has been largely ignored. To investigate this aspect of PCX, we have used the efferent pathway from mouse PCX to the orbitofrontal cortex (OFC). Using double fluorescent retrograde tracing, we identified the output neurons (OPNs) of the PCX that project to two subdivisions of the OFC, the agranular insula and the lateral orbitofrontal cortex (AI-OPNs and LO-OPNs, respectively). We found that both AI-OPNs and LO-OPNs showed a distinct spatial topography within the PCX and fewer than 10% projected to both the AI and the LO as judged by double-labeling. These data revealed that the efferent component of the PCX may be topographically organized. Further, these data suggest a model for functional organization of the PCX in which the OPNs are grouped into parallel output circuits that provide olfactory information to different higher centers. The distributed afferent input from the olfactory bulb and the local PCX association circuits would then ensure a complete olfactory representation, pattern recognition capability, and neuroplasticity in each efferent circuit. Significance The mammalian olfactory system is capable of detecting and discriminating a vast and diverse array of small organic molecules or odorants. Complex blends of these chemicals are finally perceived as a unified odor object—for example, a rose contains dozens of active compounds. The piriform cortex (PCX) is the largest component of the olfactory cortex and has been hypothesized to be the locus of odor object formation. However, the PCX shows a distributed odorant representation that contrasts sharply with the topographical representation typically seen in the other primary sensory cortices. In this article, we explore an alternative organizational principle for the PCX based on where neurons are sending their output, rather than where these neurons are receiving their input.