Memory persistence of rats in a radial maze varies with training procedure

Different estimations of the time-course of spatial working memory have been reported. Some authors found working memory in the radial maze to be relatively long lasting, while others found more rapid exponential decay. In the present experiments it was attempted to account for the conflicting results by investigating the effects of different training procedures. Two types of training were examined under the same circumstances. A group of seven rats was given a series of delayed trials (5, 20, 60, and 120 min). Every delay was repeated at least four times and the delays were presented in an ascending order. The number of errors decreased at every delay except the last one (120 min), where error levels were constant (.50 errors/trial). The good performance was not based on use of intramaze cues or response chaining. In another group of seven rats the same delays were introduced in a quasi-random order and alternated with uninterrupted trials. The number of errors increased exponentially with the length of the delay. However, when this procedure was repeated, the number of errors decreased. These results suggest that training with delayed trials is a major factor to account for the differences in reports of memory persistence in the radial maze.