THE DELAYED-CONDITIONAL-DISCRIMINATION TASK IMPROVES MEASUREMENT OF WORKING-MEMORY IN RATS

The validity of delayed-matching-to-sample (DMTS) and related tasks ex ecuted in skinner boxes as an animal model for human working memory (W M) is confounded by the occurrence of mediating behaviour during delay s. True matching, a supplementary task during delays and response simi larity are ways to deal with this problem. However, until now rats hav e not been able to learn a true matching task in Skinner boxes and int roduction of a supplementary task during delays does not sufficiently prevent mediating behaviour. Response similarity, on the other hand, e ffectively prevents the use of mediating behaviour by reducing the dis criminative value of the behaviour during delays. Furthermore, it is a rgued that the interpretation of drug effects is confounded by baselin e performance and mediating behaviour. It is shown that high baseline levels and high amounts of mediating behaviour can induce delay depend ent drug effects, suggesting a specific effect on WM. We therefore ass ert that examination of delay-dependency of a drug effect alone is not sufficient to claim specific effects of a drug on WM. The delayed-con ditional-discrimination (DCD) task uses response similarity to effecti vely reduce mediating behavior and does not generate high levels of ba seline performance. The DCD task is therefore preferred over other tas ks for the measurement of WM in rats using skinner boxes. (C) 1997 Els evier Science Ltd.