Dynamics of odor sampling strategies in mice

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.

Spatial information from the odour environment in mammalian olfaction

“…With the navigation field moving towards virtual reality setups that eliminate the relevance of olfactory cues (Harvey et al 2009), the need arises for research that specifically addresses olfactory navigation. Conventional navigation tasks using olfactory cues will benefit from employing new technologies in arena design (Findley et al 2020;Jackson et al 2020;Liu et al 2020), videotracking (Mathis et al 2018;Wiltschko et al 2015), respiration measurements (Reisert et al 2020) and odour data obtained from head-mounted sensors (Tariq et al 2019) and two-dimensional plume measurements (Connor et al 2018;Crimaldi and Koseff 2001). This research would further be enriched by olfactorybased virtual reality systems (Radvansky and Dombeck 2018) that can reproduce the richness of turbulent odour environments and also allow for subtle manipulations of the stimuli.…”

Odor sampling strategies in mice with genetically altered olfactory responses

“…We implanted mice with telemetric thoracic breathing sensors [PhysioTel TA11PA-C10, Data Sciences International (DSI) (St. Paul, USA)] to record their thoracic pressure and therefore their breathing frequency as previously described [17,50,52,53]. Mice were anesthetized with isoflurane and depth of anesthesia was tested with a toe pinch.…”

“…Methods for training the mice on the odorant detection and discrimination task are described in detail in Reisert et al [17] and are based on Slotnick & Restrepo [54]. A modified olfactometer [based on 55] with two ports was used, one odor delivery port and one to deliver water rewards [50].…”

“…We adopted a stringent protocol for both types of experiments (described in detail in [17]) to ensure that mice indeed used the odor delivered to the odor port to make their behavioral decisions, instead of other stimuli, e.g. sound or vibrational signals, emanating from the olfactometer.…”

“…Active olfactory exploration is often accompanied by an increase in breathing frequency ("sniffing"), the latter having been implicated in such diverse functions as directing odorant flow to different parts of the olfactory epithelium, increasing odorant flux to the olfactory epithelium, promoting discrimination ability, discovery of new odorants, adaptive filtering of olfactory information, encoding of olfactory information in the olfactory bulb and coordination of the olfactory system with other brain areas [2][3][4][9][10][11][12][13][14][15]. The change in breathing frequency from typically 2-5 Hz at rest to 5-10 Hz during a sniff bout in rats and mice can be triggered by the presentation of a novel odorant or in anticipation of an olfactory task with the increase in breathing frequency preceding the odorant presentation by approximately one sniff cycle [2,4,16,17]. An increase in breathing frequency is mainly achieved by shortening the exhalation phase of the sniff cycle, with the inhalation duration staying relatively constant [10].…”