Modality of odor perception is transmitted to cortical brain regions from the olfactory bulb

Odor perception is the impetus for important animal behaviors, most obviously for feeding but also for mating and communication. There are two predominate modes of odor processing: odors pass through the front of the nose (orthonasal) while inhaling and sniffing, or through the rear (retronasal) during exhalation and while eating. Despite the importance of olfaction for an animal’s well-being and specifically that ortho and retro naturally occur, it is unknown how the modality (ortho versus retro) is even transmitted to cortical brain regions, which could significantly affect how odors are processed and perceived. We show mitral cell neurons in the rat olfactory bulb reliably transmit ortho versus retro food odor stimuli. Drug manipulations affecting GABA A that control synaptic inhibition lead to worse decoding of ortho/retro, independent of whether overall inhibition increases or decreases, suggesting that the olfactory bulb circuit is naturally structured to encode this important aspect of odors. Detailed data analysis paired with a firing rate model to capture population trends in spiking statistics shows how this circuit with baseline inhibition can encode odor modality. We have not only shown that ortho versus retro information is encoded to downstream brain regions, but models and analyses reveal the network dynamics that promotes this encoding.