The Effects of Forebrain Ablations on Some Behaviors in Xenopus Laevis
In order to further elucidate the hypothesis that the telencephalon of ectothermic vertebrates functions primarily as a non-specific arousal mechanism, facilitating lower brain areas, (the Arousal Hypothesis) the South African clawed frog, Xenoous laevis, was studied in four behavioral situations before and after telencephalon ablation, olfactory bulb ablation or sham surgery. Particular attention was paid to measurements of the temporal aspects of the behaviors studied. The behaviors studied were: 1. Habituation to an acoustic-vibratory stimulus 2. The optomotor response 3. Escape from shallow water 4. Feeding behavior In the habituation experiment no changes were found in the number of responses oer session, the strength of the .responses or in the strength of the initial responses. Certain telencephalon-ablated individuals, however, showed a marked decrease in the number of responses to habituate which was not seen in any of the animals in the other groups. There were no changes in optomotor responses to moving vertical black and white stripes which were attributable to the operations. In an experiment involving escape from shallow water into deeper water, there was a significant increase in the length of time to escape in the telencenhalon ablated-group. In the feeding experiment, it was found that ablations of the telencephalon eliminated feeding behavior. It is concluded that 'arousal,' defined as that function regulating frequency and other temporal aspects of behavior (but not response strength) is the major function of the forebrain in Xenopus laevis. The telencephalon, however, does not play a major role in relatively simple behaviors.
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