Quantifying nonmnemonic strategies in two-alternative forced choice delayed matching and nonmatching-to-position tasks in mice (Musmusculus) using automated video tracking technologies

Delayed matching-to-position (DMTP) and delayed nonmatching-to-position (DNMTP) tasks are widely used as standard paradigms for evaluating working memory in rodents. In these tasks, which employ a two-alternative forced choice (2AFC) design, animals initiate each trial by nosepoking a back key, which triggers the illumination of a sample key (either the left or right front key). Upon nosepoking the sample key, a delay interval begins, during which the back key remains illuminated, requiring continuous nosepoking to suppress the use of nonmemory strategies. After the delay interval, the first nosepoke on the back key activates both front keys. Reinforcement is contingent on choosing the same key as the sample in the DMTP task, or the opposite key in the DNMTP task. Performance is typically measured as the proportion of correct responses across varying delay intervals, which generally decline as delay interval increases. However, whether the imposed mediating response (continuous nosepoking of the back key) effectively prevents the use of nonmemory strategies remains insufficiently explored. In this study, we recorded and analyzed the movements of mice during these tasks using automated video tracking. Our findings suggest that mice may rely on spatial heuristics, including mediating behaviors such as maintaining body position relative to the sample keys, rather than solely on working memory. These results challenge the assumption that DMTP and DNMTP tasks exclusively measure working memory, highlighting the need for cautious interpretation of task performance.