A non-spatial, stimulus-comparison working memory task in rats and disruption by scopolamine

Working memory is a theoretical concept referring to a set of cognitive processes that provide temporary maintenance and manipulation of the information necessary for complex cognitive tasks. The preponderance of working memory tasks emphasizes the maintenance of information, and, is spatially oriented. Working memory tasks which are not spatially oriented and which require not only the maintenance but also the manipulation of information are needed in order to further our understanding of working memory in animals. The present studies describe a non-spatial, stimulus-comparison procedure for evaluating working memory in rats which may also tap into the central executive component of working memory. The present procedure requires the animals to compare two stimuli (a light and a tone) and, after a delay, respond on one of two levers if the stimuli are the same and on the other lever if the stimuli are different. Thus, the rats must not only remember the stimuli, but must also operate on, i.e. compare, them in order to respond correctly. The rats relatively rapidly acquired the behavior in approximately 30 sessions and did not exhibit a response bias for response location or stimulus type. Moreover, the percent correct responding was dependent on the duration of the retention interval. The muscarinic cholinergic receptor antagonist scopolamine, but not by its quaternary analog N-methyl scopolamine, decreased the percentage of correct responding as well as the discriminability of the stimuli as measured by log d while having no effect on bias as measured by log b. The present findings are consistent with the hypothesis that the present non-spatial, stimulus-comparison procedure may be useful for evaluating working memory in a manner which may involve the central executive component. (c) 2006 IBRO. Published by Elsevier Ltd. All rights reserved.