Mice showed odor-induced reward-predictive licking behavior proportional to expected reward size. Mice showed odor-induced reward-predictive licking behavior proportional to expected reward size. A, Schematic illustration of the behavioral apparatus. Mice were restricted, head and body, by the metal frame and tube. The odor mask, water spout, and air-puff tube were set in front of their noses, mouths, and eyes. Spout-licking behaviors were monitored using an infrared sensor. The miniature microscope was mounted on their heads. B, Time sequence of a classical conditioning task. C, An example of reward-predictive spout-licking behaviors after sufficient learning. In trials of reward conditions, spout-licking behaviors started during odor presentation periods. Black dots indicate spout-licking behaviors. Yellow areas show CS-delay periods. D, Daily changes of spout-licking frequency during CS-delay periods of the mouse illustrated in C. Early and late stages were defined based on the appearance of reward-predictive licking. Error bars indicate SEs. E, Average spout-licking frequencies during CS-delay periods of all eight mice. Error bars indicate SEs. Tomohiko Yoshizawa et al. eNeuro 2018;5:ENEURO.0367-17.2018 ©2018 by Society for Neuroscience