UC San Diego

Across sensory systems, active behaviors, like sniffing, gazing, and touching, gate and tailor the information that reaches the brain. For our sense of smell, main olfaction, sniffing and its role in shaping and enabling sensation have been extensively characterized. However, most land vertebrates have two olfactory senses: main and accessory olfactory systems (MOS and AOS, respectively). Because the sense organ of the AOS, the vomeronasal organ (VNO), is nonfunctional in humans and anatomically inaccessible in behaving animals, when and how the VNO is engaged and whether animals actively govern vomeronasal sensation have remained unknown. Here we use head-mounted miniscopes to image VNO activity in freely behaving mice and show that sensation is sparse and entirely gated by a previously undescribed, rapid (~30-millisecond) nose movement we call narial pad dabbing. The dabbing action is volitional and purposefully deployed, directed by the MOS. A single dab activates stimulus-specific ensembles sufficient to identify closely related stimuli and trigger innate behavior; sustained bouts exploit sensory adaptation to reshape the active ensemble over time. Mice scale dabbing depending on stimulus identity, concentration, and the receiver’s sex-hormone state. Thus, using a previously undescribed active sampling behavior, mice actively control when, where, and how intensely to use the VNO. These findings recast the AOS not as a redundant or vestigial companion to smell, but as a cooperative sensory channel purpose-built to deliver slow, persistent chemosensory information on a timescale potentially designed for computations in the brain's subcortical circuits.