Supplementary Figure 1: Olfactometer for behavioral experiments.

A custom built olfactometer was used to deliver mixtures of odorants to the mouse. The olfactometer was designed to allow each of the 16 odorants to be present or absent in any mixture while keeping the concentration of each odorant independent of other odorants. a. To achieve this goal, the olfactometer was built with 16 modules, each controlling one odorant and contributing a constant and equal amount to the output flow. Input flow into the modules and output flow from the modules were made using FEP-lined Tygon/PVC tubing connected in symmetric pair-wise bifurcations. Each module had a 3-way valve (Lee Company, USA) that diverted the input flow of clean air to go through either of two glass tubes, one containing the odor and solvent and one containing only the solvent. Both pathways then converged to form the module output flow. From the point where all odorants converged to the odor port, the odorous air flowed through a 4 foot long tubing of 1/16 inch diameter. This minimized the latency from valve opening to odor presentation and ensured mixing of the odorants to at least within the scale of the tubing. Odorant mixtures were generated by controlling the 16 module valves allowing 2¹⁶ possible mixtures. b. Photoionization detector (miniPID, Aurora Scientific) measurements were used to analyze the output of the olfactometer. The amplitude of the PID signal in response to an odorant mixture was equal to the sum of the amplitudes of PID signals in response to the individual components, indicating that the different odorant modules are independent.