Release from proactive interference in rat spatial working memory.

A three-phase procedure was used to produce proactive interference (PI) in one trial on an eight-arm radial maze. Rats were forced to enter four arms for reward on an initial interference phase, to then enter the four remaining arms on a target phase, and to then choose among all eight arms on a retention test, with only the arms not visited in the target phase containing reward. Control trials involved only the target phase and the retention test. Lower accuracy was found on PI trials than on control trials, but performance on PI trials significantly exceeded chance, showing some retention of target memories. Changes in temporal and reward variables between the interference, target, and retention test phases showed release from PI, but changes in context and pattern of arm entry did not. It is suggested that the release from PI paradigm can be used to understand spatial memory encoding in rats and other species.