Behavioral discrimination and olfactory bulb encoding of odor plume intermittency

In order to survive, animals often need to navigate a complex odor landscape where odors can exist in airborne plumes. Several odor plume properties change with distance from the odor source, providing potential navigational cues to searching animals. Here, we focus on odor intermittency, a temporal odor plume property that measures the fraction of time odor is present at a given point within the plume and decreases with increasing distance from the odor source. We sought to determine if mice are capable of using changes in intermittency to locate an odor source. To do so, we trained mice on an intermittency discrimination task. We establish that mice can discriminate odor plume samples of low and high intermittency and that the neural responses in the olfactory bulb can account for task performance and support intermittency encoding. Modulation of sniffing, a behavioral parameter that is highly dynamic during odor-guided navigation, affects both behavioral outcomes on the intermittency discrimination task as well as neural representation of intermittency. Together, this work demonstrates that intermittency is an odor plume property that can inform olfactory search and more broadly supports the notion that mammalian odor-based navigation can be guided by temporal odor plume properties.

Methods
Mice were tested to see if they could discriminate different levels of odor intermittency (an odor plume property). Labview was used to run the tests. The RedShirtImaging Neuroplex and NeuroCCD system was used for concomitant optical imaging of the dorsal olfactory bulb in the head-fixed mice. Half the mice expressed G-CamP6f in olfactory receptor neurons, the other half in post-synaptic mitral/tufted cells. Matlab was used to analyze the behavioral and neural glomerular data. Another set of mice was similarly optically imaged under anesthesia to systematically assess neural coding across the dorsal olfactory bulbs of odor intermittency as a function of sniff rate.