The effects of an intramaze cue search rule on rat's spatial working memory.

Two groups of rats were trained in an elevated 8-arm radial maze consisting of four smooth and four hardware cloth covered (grid) arms. Rats in one group (Texture Relevant) had to enter four baited arms of one texture, Set A, before they could be rewarded for entering the second set of arms of the other texture, Set B. Rats in the other group (Texture Irrelevant) were not constrained in their pattern of arm selection. Rats in both groups were run in the maze until they had sampled all baited arms. Although Texture Relevant (TR) rats initially made more reentries than Texture Irrelevant (TI) rats during the first training phase, rats in both groups reduced reentries to equivalent, low asymptotic levels. TR rats also made many premature entries to Set B arms during initial training but reduced these errors with continued training. When adjacent arms became less spatially differentiated with reference to extramaze room stimuli in the second phase and in a replication of this experiment, TI rats increased reentries to earlier sampled arms more than TR rats. TR rats, however, increased premature entries into Set B when arms within each texture set became less spatially differentiated with respect to extramaze room stimuli. These results indicate that TR rats developed a stable hierarchical representation of the maze, which enhanced their retention of earlier visited arms in more difficult maze configurations.