The ability to catch scent continuously while running, which may be an essential skill for many animals of prey, requires that ambient air flows inward through the nose also during expiration. In this study on bird dogs, the direction of air flow was detected by measuring the temperature in the air inside the nostril. While resting, nose ventilation was synchronous with lung ventilation. While searching for ground scent, the dog was sniffing at a frequency of up to 200 s-1, a strategy which may create turbulence in the nasal passages and thereby enhance transport of scent molecules to the receptors in the ethmoidal cavity. When the bird dog was searching for game while running with its head high against the wind, it maintained a continuous inward air stream through the nose for up to 40s spanning at least 30 respiratory cycles. We suggest that expiratory gas flowing at high velocity from the trachea to the mouth cavity creates a lower pressure than in the nose thus causing an inward air stream through the nose during expiration by a Bernoulli effect.
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"I N T R O D U C T I O N Sniffing is a voluntary inhalation of air through the nose, typically expressed in the context of odor sampling. Most mammals studied—including humans (Johnson et al. 2003; Laing 1982; Porter et al. 2007; Sobel et al. 2000), dogs (Steen et al. 1996; Thesen et al. 1993), rats (Welker 1964; Youngentob et al. 1987), mice (Sorwell et al. 2008; Wesson et al. 2008b; Youngentob 2005), hamsters (Macrides 1975), rabbits (Freeman et al. 1983; Karpov 1980; Pager 1985) and even semiaquatic shrews (Catania et al. 2008)—alter their sniffing behavior when investigating odors. Furthermore, rhythmic odor sampling behaviors analogous to sniffing are shown by terrestrial and aquatic nonmammalian vertebrates and invertebrates (Budick and Dickinson 2006; Goldman and Patek 2002; Nevitt 1991; Schmitt and Ache 1979). "
[Show abstract][Hide abstract]ABSTRACT: Many mammals display brief bouts of high-frequency (4-10 Hz) sniffing when sampling odors. Given this, high-frequency sniffing is thought to play an important role in odor information processing. Here, we asked what role rapid sampling behavior plays in odor coding and odor discrimination by monitoring sniffing during performance of discrimination tasks under different paradigms and across different levels of difficulty and by imaging olfactory receptor neuron (ORN) input to the olfactory bulb (OB) during behavior. To eliminate confounds of locomotion and object approach, all experiments were performed in head-fixed rats. Rats showed individual differences in sniffing strategies that emerged during discrimination learning, with some rats showing brief bouts of rapid sniffing on odorant onset and others showing little or no change in sniff frequency. All rats performed with high accuracy, indicating that rapid sniffing is not necessary for odor discrimination. Sniffing strategies remained unchanged even when task difficulty was increased. In the imaging experiments, rapid sniff bouts did not alter the magnitude of odorant-evoked inputs compared with trials in which rapid sniffing was not expressed. Furthermore, rapid sniff bouts typically began before detectable activation of ORNs and ended immediately afterward. Thus rapid sniffing did not enable multiple samples of an odorant before decision-making. These results suggest that the major functional contribution of rapid sniffing to odor discrimination performance is to enable the animal to acquire the stimulus more quickly once it is available rather than to directly influence the low-level neural processes underlying odor perception.
Full-text · Article · Feb 2009 · Journal of Neurophysiology
"To provide a quantitative and more concrete description of sniffing in mice, we chose to focus our analysis on sniff frequency. Sniff frequency has been widely used as a descriptor of sniffing behavior in other animals (Welker 1964; Youngentob et al. 1987; Thesen et al. 1993; Steen et al. 1996; Kepecs et al. 2007), and sniff timing (rather than waveform) is the major parameter considered in current models of how sniffing shapes olfactory processing (Macrides 1975; Kepecs et al. 2006; Wachowiak and Shipley 2006; Verhagen et al. 2007; Bathellier et al. 2008). During free exploration of a novel environment, sniffing behavior was unstructured, with rapid transitions from low-frequency but irregular sniffing to bouts of highfrequency sniffing lasting usually less than 2 s and reaching sustained rates of ;10 Hz. "
[Show abstract][Hide abstract]ABSTRACT: Sniffing, a rhythmic inhalation and exhalation of air through the nose, is a behavior thought to play a critical role in shaping how odor information is represented and processed by the nervous system. Although the mouse has become a prominent model for studying olfaction, little is known about sniffing behavior in mice. Here, we characterized mouse sniffing behavior by measuring intranasal pressure transients in behaving mice. Sniffing was monitored during unstructured exploratory behavior and during performance of 3 commonly used olfactory paradigms: a habituation/dishabituation task, a sand digging-based discrimination task, and a nose poke-based discrimination task. We found that respiration frequencies in quiescent mice ranged from 3 to 5 Hz--higher than that reported for rats. During exploration, sniff frequency increased up to approximately 12 Hz and was highly dynamic, with rapid changes in frequency, amplitude, and waveform. Sniffing behavior varied strongly between tasks as well as for different behavioral epochs of each task. For example, mice performing the digging-based task showed little increase in sniff frequency prior to digging, whereas mice performing a nose poke-based task showed robust increases. Mice showed large increases in sniff frequency prior to reward delivery in all tasks. Mice also showed increases in sniff frequency when nose poking in a nonodor-guided task. These results show that mouse sniffing behavior is highly dynamic, varies with behavioral context, and is strongly modulated by olfactory as well as nonolfactory events.
"Animals often rely on olfactory cues to discriminate between friends and foes, danger and shelter, or fresh and rotten foods. Few studies have examined sniffing during such an olfactory discrimination process in its ethological context (Thesen et al., 1993; Steen et al., 1996). One notable study showed that dogs can reliably track footprints outdoors by sniffing at 6 Hz 10–20 times in a bout to find the track, then slow down to take 30–40 sniffs at 2–5 footprints to decide a track's direction (Thesen et al., 1993). "
[Show abstract][Hide abstract]ABSTRACT: Sniffing is a rhythmic motor process essential for the acquisition of olfactory information. Recent behavioral experiments show that using a single sniff rats can accurately discriminate between very similar odors and fail to improve their accuracy by taking multiple sniffs. This implies that each sniff has the potential to provide a complete snapshot of the local olfactory environment. The discrete and intermittent nature of sniffing has implications beyond the physical process of odor capture as it strongly shapes the flow of information into the olfactory system. We review electrophysiological studies-primarily from anesthetized rodents-demonstrating that olfactory neural responses are coupled to respiration. Hence, the "sniff cycle" might play a role in odor coding, by allowing the timing of spikes with respect to the phase of the respiration cycle to encode information about odor identity or concentration. We also discuss behavioral and physiological results indicating that sniffing can be dynamically coordinated with other rhythmic behaviors, such as whisking, as well as with rhythmic neural activity, such as hippocampal theta oscillations. Thus, the sniff cycle might also facilitate the coordination of the olfactory system with other brain areas. These converging lines of empirical data support the notion that each sniff is a unit of olfactory processing relevant for both neural coding and inter-areal coordination. Further electrophysiological recordings in behaving animals will be necessary to assess these proposals.