International Journal of Comparative Psychology

The effects of ablation of the corpus, eminentia granularis and valvula of the cerebellum on the performance of optomotor tasks, and the appearance of atypical behavior patterns were studied in the teleost fish Aquidens latifrons . The subjects were observed in their home tanks before and after surgery, and were tested in a modified optomotor apparatus where the drum changed direction of rotation at regular intervals. The corpus cerebellum was ablated totally or partially, bilaterally or unilaterally. In other subjects the eminentia granularis was ablated on the right side or in conjunction with ipsilateral corpus lesions. The valvula was completely ablated in still other subjects with only slight damage to adjacent brain tissue.

When experimentally naive intact fish were given a series of optomotor tests they gradually improved their optomotor performance. After cerebellar operations this improvement was reversed in most of the optomotor measurements as the fish followed the moving stripes much less efficiently. However swimming speed, which we considered a good indicator of motor performance, was unchanged except in 2 out of 13 groups. We concluded that the less efficient optomotor behavior could not be attributed to a direct effect of the lesions on motor processes. The home-tank observations clearly revealed four postoperative motor abnormalities. Oscillatory movements, wobbling and tilting persisted through the tests, but the fourth, lying on the side, a more profound disability, disappeared in all but one subject in a few hours to a few days. The first three abnormal behavior patterns, especially the oscillatory movements, suggest a deficiency in fme motor tasks and support the interpretation that the major function of the cerebellum is described best as the modulation of movement. High levels of tilting and lying on the side in subjects with unilateral lesions maybe caused by an inbalance in motor function. Several alternative or additional functions of the cerebellum suggested by these experiments are evaluated.