Neural Mechanisms and Behavior in Unrestrained Mouse Olfactory Search
Date
2020-12-08
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University of Oregon
Abstract
For many organisms, searching the environment for food and mates entails active sensing. Finding odorous targets may be the most ancient search problem that motile organisms have evolved to solve. While chemosensory navigation has been well characterized in micro-organisms and invertebrates, spatial olfaction in vertebrates is poorly understood. Here, we developed an olfactory search assay where freely moving mice must navigate turbulent airborne odor gradients. Mice are concentration gradient-guided and do not rely upon stereo olfaction to successfully search these gradients. Further, mice synchronize head movement with sniffing with 10s of milliseconds precision. Using unsupervised machine learning, we identified 11 behavioral motifs that make up the structure of search behavior in this task. The onset of these motifs align tightly with the sniff cycle. These motifs sort into two broad categories of search based on nose speed and sniff synchronization. We have defined these two categories as investigation and approach. This assay lays the foundational behavioral work to investigate the underlying neural mechanisms of olfactory search.
Movement is pervasively encoded across the brain and sampling movements dictate future sensory input. We anticipate that features of sampling movement are therefore encoded in early sensory areas such as the olfactory bulb. We designed an experimental assay that accommodates chronic local field potential recordings in olfactory bulb in the unrestrained mouse to investigate how olfactory bulb signals encode movement during olfactory search. Our system executes 3-dimensional tracking with high accuracy and can be generalized to accommodate many experimental techniques (electrophysiology, fiber photometry, optogenetics, etc.). This tracking is precisely aligned at the millisecond time scale with 16 channel electrophysiological recordings in the olfactory bulb and sniffing from an intranasally implanted thermistor. This assay development will accommodate future experiments into the neural mechanisms of olfactory search behaviors.
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Keywords
active sensing, animal behavior, navigation, olfaction, olfactory bulb