Figure 1

Delayed alternation task in Y-maze. The Y-maze consisted of a start box and two arms (left and right). Inside the maze were installed seven infrared beams, marked by #1 through #7. Each trial was started by rats’ breaking the infrared beam #1 in the start box. After a delay of 6 seconds, the start-box door was opened and rats were allowed to visit the two arms. If rats had chosen the left arm in the previous trial, they were required to select the right arm in the present trial, or vice versa. Thus, rats had to remember the arm they had visited in the previous trial in order to make a correct choice in the present trial. After consuming the water reward at the reward site, rats ran back to the start box to initiate the next trial.