An isolation effect in rat spatial memory.

Rats' working memory for locations previously visited and not visited was tested on the radial maze. Trials consisted of a study phase followed by a test phase. In the study phase, rats were forced to visit half the arms on the maze, with the other half of the arms blocked. In the test phase, rats chose among all arms. with food found only on the arms not visited in the study phase. When different patterns of arms visited in the study phase were used, it was found that rats remembered an alternating pattern better than an adjacent pattern or a random pattern and that this effect became more pronounced at longer retention intervals. In addition, rats remembered isolated nonvisited arms in the random pattern that were sandwiched between visited arms better than nonvisited arms that were not isolated between visited arms. Several hypotheses were examined and tested to explain this isolation effect, but no clear theoretical account was found.