Nonrecurring-items delayed nonmatching-to-sample in rats: A new paradigm for testing nonspatial working memory

Rats were trained on a nonrecurring-items delayed nonmatching-to-sample task, using a newly designed apparatus and a training protocol similar to that used in experiments on nonspatial working memory in humans and monkeys. On each trial, the rats were briefly presented with a sample object, which was presented again along with another object after a delay; the rats were rewarded with food if they chose the novel object. New stimuli were used on each trial. With delays of 4 sec between the sample and choice runs, the rats learned the task to 90% accuracy in less than 250 trials. When the delay was subsequently increased to 15, 60, 120, and 600 sec, the rats scored approximately 91%, 81%, 77%, and 57%, respectively. These results establish that rats are capable of excellent performance on a nonspatial working-memory task that is comparable to those commonly used in monkey models of amnesia, and they suggest that the nonrecurring-items delayed nonmatching-to-sample paradigm may prove valuable in modeling brain-damage-produced amnesia in rats.