Figure 1.

Task design. A, Schematic illustration of the experimental chamber. The chamber was equipped with three holes for nose poking (L, left hole; C, center hole; R, right hole) and a pellet dish (D). B, Time sequence of choice tasks. After a rat poked its nose into the center hole, one of three cue tones was presented. The rat had to maintain the nose-poke in the center hole during presentation of the cue tone. After offset of the cue tone, the rat was required to perform a nose-poke in either the left or right hole and then either a reward tone or a no-reward tone was presented. The reward tone was followed by delivery of a sucrose pellet in the food dish. The reward probability was determined by the given cue tone and the chosen action. C, The reward probabilities for cue tones and actions. For the left tone, the reward probabilities were (left, right) = (50%, 0%). For the right tone, the probabilities were (left, right) = (0%, 50%). These probabilities were fixed throughout the experiments. For the choice tone, reward probabilities were varied: one of four pairs of reward probabilities [(left, right) = (90%, 50%), (50%, 90%), (50%, 10%), and (10%, 50%)] were used for each block.