| Abstract: | Rats were trained in an eight-arm radial maze and tested using a proactive interference (PI) procedure. Each test trial consisted of forced choices of four randomly selected arms followed, after a 2-h delay, by free choices among all eight arms. Normally, rats chose correctly during the free choices by entering and retrieving food from the four arms not yet visited during the test trial. Occasionally, an interference trial preceded the test trial by 1.5 or 3 h; interference trials consisted of forced choices of another four arms and an immediate test. The presence of an interference trial lowered test-trial performance (PI). Electroconvulsive shock (ECS) administered immediately after the interference trial had no effect; i.e., PI was still observed. When ECS was administered at the midpoint of the 3-h intertrial interval, performance increased to control (no ECS, no PI) levels. Such release from PI, however, was not obtained, and test-trial performance remained inaccurate when ECS was delivered immediately after the forced choices of the test trial (either 1.5 or 3 h after the interference trial). |
