Remembrance of places lasts: Proactive inhibition and patterns of choice in rat spatial memory

Abstract

A series of experiments was carried out to evaluate the notion that rats given a sequence of massed daily trials on the radial maze reset working memory at the end of each trial by deleting its contents. Although curves presented by D. S. Olton [ Scientific American, 1977 , 236, 82–98; In S. H. Hulse, H. Fowler, & W. K. Honig (Eds.), Cognitive processes in animal behavior, Hillsdale, N.J.: Erlbaum, 1978] show that rats return to errorless performance at the beginning of each trial after the first, the fact that accuracy falls less rapidly over choices on Trial 1 than on subsequent trials suggests a proactive inhibition (PI) effect. In Experiment 1, Olton's findings were replicated, and a PI effect was observed on Days 1–2 of testing. On Days 3–5, overall accuracy improved significantly and was associated with the development of a strong tendency for rats to enter adjacent alleys, which became particularly marked on the final trials of a day's testing. In order to prevent rats from achieving accurate performance by using an adjacent alleys pattern, a procedure was used in Experiment 2 which involved initial forced random choices followed by a retention test consisting of free choices. Repeated daily trials with this procedure yielded a significant PI effect, which was more marked at a 60-sec delay than at a 0-sec delay. Experiments 3 and 4 showed this PI effect to be robust and resistant to manipulations designed to produce release from PI. Both the PI effect and a strong tendency found in Experiment 1 for animals to avoid on the initial choices of Trial n those alleys most recently entered on Trial n−1 argue that rats do not reset working memory between trials.