Abstract

Object-recognition memory has been assessed in rats using the delayed non-matching-to-sample (DNMS) task and the novel-object preference (NOP) test. The DNMS task provides an accurate measure of rats’ object-recognition abilities, however, the conventional procedures are not practical because rats require extensive training to reach peak performance and object-recognition memory can only be assessed using retention intervals of up to a few minutes. The NOP test does not require rats to be trained in advance, and for this reason it has become widely popular as a test of object-recognition memory. Recent findings, however, question the internal validity of the NOP test, namely its assumption that the strength of novelty preference corresponds directly to the strength of the memory for an object. The goal of the present study was to develop a new test of object-recognition memory. The new method incorporates the appetitive-reward and explicit choice aspects of the DNMS task and it employs a circular-track apparatus that has been previously used in a modified NOP test. Rats’ performance on the new task was similar to the levels of accuracy reported on conventional DNMS tasks but were achieved in far fewer trials than conventional DNMS tasks. When the delay was increased, performance decreased slightly but remained significantly above chance. Additionally, we compared rats’ performance on the new task to their scores on the NOP test and did not find a consistent linear relationship. The results from this new task confirm its utility as a test of object-recognition memory in rats, while challenging the assumption that the strength of novelty preference on the NOP test corresponds to the strength of memory for an object.