Coordination of Orofacial Motor Actions into Exploratory Behavior by Rat

The delineation of sensorimotor circuits that guide exploration begins with an understanding of the pattern of motor outputs [1]. These motor patterns provide a clue to the form of the underlying circuits [2-4] (but see [5]). We focus on the behaviors that rodents use to explore their peripersonal space through goal-directed positioning of their nose, head, and vibrissae. Rodents sniff in response to novel odors, reward expectation, and as part of social interactions [6-12]. Sniffing serves olfaction [13, 14], while whisking synchronized to sniffing serves vibrissa-based touch [6, 15, 16]. We quantify the ethology of exploratory nose and head movements in relation to breathing. We find that sniffing is accompanied by prominent lateral and vertical deflections of the nose, i.e., twitches, which are driven by activation of the deflector nasi muscles [17]. On the timescale of individual breaths, nose motion is rhythmic and has a maximum deflection following the onset of inspiration. On a longer timescale, excursions of the nose persist for several breaths and are accompanied by an asymmetry in vibrissa positioning toward the same side of the face. Such directed deflections can be triggered by a lateralized source of odor. Lastly, bobbing of the head as the animal cranes and explores is phase-locked to sniffing and to movement of the nose. These data, along with prior results on the resetting of the whisk cycle at the onset of inspiration [15, 16, 18], reveal that the onset of each breath initiates a "snapshot" of the orofacial sensory environment. VIDEO ABSTRACT.