Beta-adrenergic control of the water permeability of the skin during rehydration in the toad Bufo arenarum

Incentive or habit learning in amphibians?

Toads (Rhinella arenarum) received training with a novel incentive procedure involving access to solutions of different NaCl concentrations. In Experiment 1, instrumental behavior and weight variation data confirmed that such solutions yield incentive values ranging from appetitive (deionized water, DW, leading to weight gain), to neutral (300 mM slightly hypertonic solution, leading to no net weight gain or loss), and aversive (800 mM highly hypertonic solution leading to weight loss). In Experiment 2, a downshift from DW to a 300 mM solution or an upshift from a 300 mM solution to DW led to a gradual adjustment in instrumental behavior. In Experiment 3, extinction was similar after acquisition with access to only DW or with a random mixture of DW and 300 mM. In Experiment 4, a downshift from DW to 225, 212, or 200 mM solutions led again to gradual adjustments. These findings add to a growing body of comparative evidence suggesting that amphibians adjust to incentive shifts on the basis of habit formation and reorganization.

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.