Abstract

Mammalian olfactory receptor neurons in the nasal cavity are stimulated by odorants carried by the inhaled air and their activation is therefore tied to and driven by the breathing or sniffing frequency. Sniffing frequency can be deliberately modulated to alter how odorants stimulate olfactory receptor neurons, giving the animal control over the frequency of odorant exposure to potentially aid odorant detection and discrimination. We monitored sniffing behaviors and odorant discrimination ability of freely-moving mice while they sampled either decreasing concentrations of target odorants or sampled a fixed target odorant concentration in the presence of a background of increasing odorant concentrations, using a Go-NoGo behavioral paradigm. This allowed us to ask how mice alter their odorant sampling duration and sampling (sniffing) frequency depending on the demands of the task and its difficulty. Mice showed an anticipatory increase in sniffing rate prior to odorant exposure and chose to sample for longer durations when exposed to odorants as compared to the solvent control odorant. Similarly, mice also took more odorant sampling sniffs when exposed to target odorants compared to the solvent control odorant. In general, odorant sampling strategies became more similar the more difficult the task was, e.g. the lower the target odorant concentration or the lower the target odorant contrast relative to the background odorant, suggesting that sniffing patterns are not preset, but are dynamically modulated by the particular task and its difficulty.

Highlights

  • It is clear that the dynamics of odor sampling during the first few sniffs taken by rodents during an odor identification task can provide enough information to allow odor identification and discrimination [1,2,3]

  • The temporal dynamics of olfactory receptor neuron (ORN) responses during odor sampling is a critical determinant of the information available to the olfactory bulb [11,12,13] or its analog, the antennal lobe in insects [14]

  • The mice showed near 100% accuracy at a propanol concentration of 10−4% concentration, which began to decline with declining odorant concentration and showed accuracy near chance, equivalent to that elicited by the odor of the mineral oil (MO) vehicle at 10−6.5%

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Summary

Introduction

It is clear that the dynamics of odor sampling during the first few sniffs taken by rodents during an odor identification task can provide enough information to allow odor identification and discrimination [1,2,3]. The importance of odor sampling by active sniffing for olfactory perception by humans and rodents has been known for more than three decades [4,5,6,7,8]. Active sniffing or odor sampling strategies dramatically alter synaptic interactions in the olfactory bulb, the first central synaptic processing site for odor-elicited sensory input [9,10]. The temporal dynamics of olfactory receptor neuron (ORN) responses during odor sampling is a critical determinant of the information available to the olfactory bulb [11,12,13] or its analog, the antennal lobe in insects [14].

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