Photoionization detector

Odorants (Sigma-Aldrich) were diluted from saturated vapor with cleaned air using a flow dilution olfactometer described previously^{43 (link)}. The olfactometer was designed to provide a constant flow of air blown over the nares. Odorants were constantly injected into the olfactometer, but sucked away via a vacuum that was switched off during odorant presentation. Cross contamination was avoided by using separate Teflon tubing for each odorant. Odorants were typically delivered at different concentrations between 0.12 and 11% of saturated vapor, although the odorant methyl valerate was also delivered at 0.04% in one preparation (Supplementary Fig. 2), and ~16% in another (Supplementary Fig. 3). The Odorants ethyl tiglate (Fig. 1), methyl valerate (Fig. 2 and Supplementary Figs 1–3) or isoamyl acetate were used for the experiments measuring both input and output in the same preparation (details for each measurement are included in Supplementary Table 2). Methyl valerate, 2-heptanone, and isoamyl acetate were used for the data in Fig. 5 that compared the output maps evoked by different Odorants. A photo-ionization detector (Aurora Scientific, Aurora, ON) was used to confirm the time course and relative concentrations presented with our olfactometer. The PID was placed next to the mouse’s nose during the optical recordings.