Symposium 4: Current Issues in Animal Learning Theories
چکیده
intensity of searching for the old goal during the probe trial. We made two significant observations. First, escape performance in normal mice appears largely determined by the ease with which they give up "non cognitive" strategies such as thygmotaxis and spatial passivity. Second escape performance is not correlated with factor 3, indicating that the spatial bias developed for the goal site can only be assessed by probe trials and not by measuring escape performance during learning. Even parameters that are designed to assess specifically the goal-directedness of the swim path during learning such as cumulative search error, Whishaw's error, and % of time spent in the goal quadrant, mainly describe factor and have little predictive value for the probe trial. Thus, factor analysis can be used to dissect spatial and alternative strategies in the water maze. Research in our laboratory on classical conditioning in rats has documented several effects of context on performance after extinction. In classical conditioning, a simple form of associative leaming that involves learning, memory, and emotion, a conditioned stimulus (CS) is first paired with an unconditioned stimulus (US), such as mild footshock. The CS therefore evokes performance. In extinction, that performance goes away when the CS is presented repeatedly on its own. In reinstatement, simple exposure to the US after extinction causes a recovery of extinguished responding provided it occurs in the context in which testing also occurs. In renewal, extinguished conditioned responding also recovers when the CS is tested in the context of conditioning after extinction has been conducted in another context. Together, these effects suggest that extinction does not destroy the original learning, but instead creates a CS whose current response response depends fundamentally on knowledge about the current context. Extensive behavioral research has suggested, however, that the two effects are mediated by different kinds of context knowledge. Reinstatement is mediated by simple context-US associations formed during US exposure. Renewal, in contrast, is controlled by the animal learning that different contexts signal or retrieve different CS-US relations. The two effects also differ in their dependence on the hippocampus, a brain structure that has long been implicated in context learning. Electrolytic lesions of the fornix (a major output pathway of the hippocampus) or neurochemical lesions of the hippocampus itself both abolish the reinstatement effect. That is, rats given either type of lesion before training show no recovery of extinguished performance when exposed to the unconditioned …