Schematic diagrams of the odor presentation system. A: Experimental set-up for orthonasal odor presentation. The olfactometer was connected to an odor nozzle and presented odor stimuli to the mouse’s nose. The upper cannula was connected to a flow meter and a vacuum pump, which controlled nasal airflow rates. The lower cannula accessed the lower trachea and remained open for normal breathing. B: Experimenatal set-up for retronasal odor presentation. The olfactometer was connected to a three-way valve and presented odor stimuli through the upper cannula. Our set-up permitted reciprocal switching of orthonasal and retronasal delivery modes in the same animal.