Fig. 1.

a Schematic diagram of the testing box. Rats were tested in a white box (88 × 42 × 30 cm, L × W × H). A removable divider was inserted into the box 29 cm from one end of the box, and the rat was placed in this holding area prior to the initiation of a trial. A single bedding-filled pot was placed in the center of the testing area while rats were shaped to dig. During exemplar training and subsequent testing, the experimenter placed two stimulus pots in the distal end of the box approximately 20 cm apart and segregated these pots by insertion of a second removable divider. When the test stimuli were ready, the divider separating the holding area from the testing area was removed, and the rat was allowed to investigate the test pots. Response latencies were recorded from the time this divider was removed until the rat displaced digging media in one of the pots. The first four trials of any discrimination were discovery trials designed to facilitate learning. On these trials, rats were given a 90-s limited hold to make a response. Additionally, if the subject made an incorrect first choice, the barrier between pots was removed and he was allowed to explore the second, correct pot to retrieve the reinforcer before test stimuli were removed from the box. On subsequent trials, the limited hold was abbreviated to 60 s. In the case of an incorrect choice on these trials, both pots were immediately removed from the testing box and the animal received no reinforcement. After the removal of the test stimuli, a divider was inserted into the box so the test area became the holding area for the subsequent trial. A subject remained here until test stimuli were readied in the distal end of the box and the next trial began. The side of reinforcement was randomly assigned to either the left or right side of the testing area. b A timeline of drug injection and post-injection testing are shown. Upon completion of the ID, rats were injected with atomoxetine. ED testing began 30 min later. Upon completion of ED testing, Rev3 was performed. The test of learned irrelevance (L-IRR) was complete immediately after Rev3. Rats required 30.6±1.2 min (mean ± SEM) to complete all post-injection tests