Target-dependent routing of sensory information in the olfactory system

Parallel processing, the ability to split the information content of sensory stimuli and handle them simultaneously, is essential for sensory perception in many systems. Mitral (MCs) and tufted cells (TCs) in the olfactory bulb (OB), with their separate but overlapping projection areas, provide an ideal anatomical basis for parallel processing. Whether they convey different information to distinct areas of the olfactory cortex remains unclear. Here, we separated mouse OB output neurons by innervation area using retrograde tracing from the anterior olfactory nucleus (AON) or the anterior piriform cortex (APC). In vivo 2-photon calcium imaging in the OB revealed projection area-dependent differences, with APC-projecting neurons coding more strongly for odor concentration and more selectively for odor identity. This separation became more pronounced when differentially traced populations were split by cell type, with APC TCs displaying the strongest concentration-dependent changes in response and AON TCs showing very promiscuous odor tuning. Purely cell-type-derived properties did not explain the projection target-dependent differences in odor representation, as both mitral and tufted cells showed similar changes, and SVM classifier analysis demonstrated that classification by projection target outperformed classification by cell type. Our data suggests a prominent projection-defined separation of sensory information in the OB.