Function of forebrain and cerebellum in learning in the teleost Tilapia heudelotii macrocephala. Bulletin of the AMNH ; v. 142, article 2

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New York : [American Museum of Natural History]
"The function of the forebrain and the cerebellum in learning in the teleost fish Tilapia heudelotii macrocephala was studied. An avoidance conditioning paradigm with light or sound as the CS and shock as the US was used. The design of the four experiments performed was: Experiment I -- operations performed prior to training; forebrain ablated in experimental subjects; sham operations performed or olfactory bulbs ablated in controls; CS was light. Experiment II -- operations performed prior to training; forebrain ablated in experimental subjects; sham operations performed on controls; CS was sound. Experiment III -- operations performed after training; subjects first underwent sham operation and then olfactory bulb ablation, or only the latter; following a period of retesting, both lobes of the forebrain were ablated; CS was sound. Experiment IV, a and b -- operations performed prior to training; body of the cerebellum ablated in experimental subjects; sham operations performed on controls; CS was light. All subjects were trained to avoid or escape from intermittent shock by swimming through a hole in a partition that divided the test tank into two equal compartments. Intact, sham, and olfactory bulb-ablated controls quickly learned to avoid the shock, and performance was stabilized soon after, with a high percentage of avoidance responses and consistently low latencies. These were achieved by the efficient intertrial behavior of the subjects, as well as by their speed and accuracy. When the forebrain was ablated prior to training, subjects took much longer to acquire the avoidance response. Even after long periods of testing, performance remained unstable, with variable latencies and fewer avoidance responses than those of the controls. When the operations were performed after training, it was found that sham operation had no effect on performance, whereas ablation of the olfactory bulbs had only a slight, transitory effect on the performance of some subjects. Ablation of the forebrain, however, resulted in marked and long-lasting deficits. Immediately after operation, avoidances dropped to a low level with a concurrent increase in the number of trials in which subjects neither avoided nor escaped. With continued testing, the performance of some subjects of Experiments I to III improved, but none reached the consistently high levels of avoidance responses and low latencies characteristic of the performance of the controls. On the other hand the performance of a few animals deteriorated in an erratic manner. Ablation of the body of the cerebellum had, at most, only a very transitory effect on equilibrium. It did, however, result in more severe deficits in the acquisition of a conditioned avoidance response than did ablation of the forebrain. Some cerebellum-ablated subjects never avoided at all, but those that did, performed at a very low level. Even escape performance was below that of a typical forebrain operate with higher latencies and fewer responses. Unlike the forebrain operates, cerebellum-ablated subjects showed no improvement with continued testing. Results are interpreted as being consistent with our hypothesis that the forebrain acts as a facilitator of behavior which is organized in other brain centers. The subsequent improvement noted in the performance of many forebrain-ablated subjects is regarded as an indication that a compensatory process is taking place in some other part of the brain. The body of the cerebellum appears to play a more essential role in the acquisition of a conditioned avoidance response and may, in fact, be directly concerned with learning processes"--P. 201.
p. 143-208 : ill. ; 27 cm.
Includes bibliographical references (p. 202-206).