Olfactory receptor neuron responses coding for rapid odour sampling

Non‐technical summary  Odorants are transported into the nasal cavity upon air inhalation where they are detected by olfactory receptor neurons (ORNs), which transduce the odorant molecules into action potentials. The rate of stimulation thus depends on the chosen breathing frequency, which in mice ranges from 2 to 10 Hz. This poses the question how ORNs respond to rapidly changing stimulation rates. Individual mouse ORNs respond reliably to repetitive 2 Hz stimulations resembling normal breathing, but actually perform much poorer when the stimulation rate is increased to 5 Hz, which is more akin to sniffing. In this case, rarely more than 50% of the stimulations elicit any response, with an increase in odorant concentration further reducing the response rate, becoming zero at high concentrations. This counterintuitive observation can be understood in the framework of an adaptive filter, which allows the animal to selectively alter its ORN output depending on the chosen breathing rate.