Learning under partial reinforcement in the toad (Bufo arenarum): effects of lesions in the medial pallium.

Two experiments studied the adjustment of toads (Bufo arenarum) to partial reinforcement in a runway. In Experiment 1, two groups received 24 daily trials of either continuous reinforcement (CR) or 50% partial reinforcement (PR). Training parameters that facilitate the PR extinction effect (greater resistance to extinction after PR than CR training) in rats were selected. PR impaired performance during acquisition but had no effect on performance during extinction relative to CR. In Experiment 2, four groups were trained in a factorial design involving CR and PR, and a lesion of the medial pallium and a sham operation. Performance during acquisition was again impaired by PR, but the medial pallium lesions had no effect. The lesion, however, increased resistance to extinction after both CR and PR training. The results are discussed in relation to comparative research on learning and to the hypothesized homology of the amphibian medial pallium and the mammalian hippocampal formation.