Operant reversal learning task

The experiments were conducted in eight operant chambers (exterior, 17.8 cm by 15.2 cm by 18.4 cm; interior, 15.9 cm by 14.0 cm by 12.7 cm; base, 40.6 cm by 29.2 cm by 1.3 cm; Med Associates, St. Albans, VT, USA) placed in sound- and light-attenuating enclosures. Each animal was trained and tested in the same operant chamber throughout the study. The stimulus lights, house lights, and reinforcements were controlled, and responses were recorded by Med-PC software (Version 2.0 for Windows, Med Associates, VT, USA). Programs controlling the schedule of reinforcement were written using Med-State notation. In training phase, mice were first trained to press both left and right levers to obtain sugar pellets as food reward. When they reached 90% baseline learning, they were trained to respond for food on a fixed ratio 10 (FR10) schedule of reinforcement, i.e., there was a reward only if they pressed the levers 10 times in a row. After stabilization of responding to a FR10, an animal would receive reward only if they press the lever 10 times in a row and only if they press the lever that has cue light on it. Then, the reverse training was started, i.e., they would get their reward only if they pressed the lever that did not contain cue light, 10 times. The testing phase consisted of the same protocol described in the training phase. The house and stimulus lights were illuminated signaling the beginning of a 10-min period (the initial phase), during which the reinforcement contingency matched that of the previous day’s training session. After the initial phase, the house and stimulus lights were extinguished, and a 10-min time-out began. After the 10-min time-out elapsed, the house light was illuminated, and the next phase of the test session began (the reversal phase), during which the reinforcement contingency was reversed. The reversal phase consisted of trials across a 10-min period. The test session was terminated after the end of the 10-min reversal. The primary dependent measure of reversal learning was the percent correct responses. Data for percent correct responses were calculated using the number of lever presses on the correct lever divided by the total number of presses multiplied by 100.