The role of the rat prelimbic/infralimbic cortex in working memory: not involved in the short-term maintenance but in monitoring and processing functions

Contrary to human and primate, working memory in the rodent is usually considered as a simple short term memory buffer and mainly investigated using delayed response paradigms. The aim of the present study was to further investigate the role of the rat prelimbic/infralimbic cortex in different spatial delayed tasks in order to dissociate its involvement in temporary storage from other information processes, such as behavioral flexibility and attention. In experiment 1 rats were trained in a standard elimination win-shift task in a radial-arm maze after which a 1-min delay was inserted mid trial. Prelimbic/infralimbic lesions induced only a transient disruption of performance following introduction of the delay. In experiment 2, rats were trained directly in a win-shift task with a 5-min delay that was subsequently extended to 30 min. Prelimbic/infralimbic lesions did not significantly affect behavior. Nevertheless, transient disruptions of performance (correlated with lesion extent) were noted repeatedly in lesioned rats when sets of interfering events were presented. The present findings indicate that prelimbic/infralimbic cortex is not directly involved in the short term maintenance of specific information but is implicated when changes, such as sudden introduction of a delay or exposure to unexpected interfering events, alter the initial situation. It appears that working memory in rodents should be considered, as in humans and primates, to encompass both storage and monitoring functions. The present results along with previous ones strongly suggest that prelimbic/infralimbic cortex is not involved in the temporary on-line storage but rather in the control of information required to prospectively organize the ongoing action.