Neurovestibular Physiology in Fish

Abstract

The vestibular system of the fish is in its essential functions homologous to that of humans. Much fundamental anatomical and physiological knowledge of the vestibular system has been obtained from study of the system in fish. In microgravity studies in spaceflight, aircraft parabolic flight, and a balloon experiment, fish have been used as experimental subjects in view of the ease of holding and handling fish. Abnormal swimming behavior of fish in weightlessness can be explained by the loss of otolith function but the same behavior shown by labyrinthectomized fish in microgravity during parabolic flight indicates the role of other gravity sensors such as the swimming bladder and the lateral line organs. The central adaptation process in fish resembles that in space motion sickness. In the context of equilibrium orientation and postural adjustment behavior, the dorsal light response (DLR) of fish has been investigated as a model of the visual–vestibular interaction. Experiments involving the effects of ablation of parts of the brain on the DLR indicate that the highest center operating in the visual–vestibular interaction in the DLR in the goldfish is the valvula cerebelli. Two hypotheses have been proposed to explain the mechanism of the DLR: the tonus asymmetry principle and the telotactic principle of Von Holst. The latter hypothesis, which is based on the cooperative action of both utriculi, has been shown to explain the behavior of unilaterally labyrinthectomized fish in the microgravity of parabolic flight. The vestibular action of fish in microgravity not only provides fundamental understanding of the otolithic organ but also indicates a role of other gravity sensors that supplement the action of the vestibular organ and may play a role in space motion sickness.