Reliable readout of mixture components from small populations of piriform cortical neurons

Abstract

Airborne chemicals emitted by multiple objects, mix in the air prior to reaching the nose, complicating the recognition of specific odors of interest. The olfactory system is therefore faced with the task of identifying objects in the presence of rich and often unpredictable backgrounds. Piriform cortex is thought to be the site of object recognition and scene segmentation, yet the nature of its responses to odorant mixtures is largely unknown. In this study we asked two related questions. 1) How do mixture representations relate to the representations of mixture components? And 2) Can the identity of mixture components be readout from mixture representations in piriform cortex? To answer these question, we recorded single unit activity in the piriform cortex of naive mice while sequentially presenting single odorants and their mixtures. We find that the magnitude of piriform cortical responses increases with added mixture components, and that the responses of individual neurons are well explained by a normalization model. Finally, we show that mixture components can be identified from piriform cortical activity by pooling responses of a small population of neurons. These results suggest that piriform cortical representations are well suited to perform figure-background segmentation without the need for learning.