NEUROPHYSIOLOGICAL BASIS OF VISUAL INNATE RELEASING MECHANISMS IN FROGS

By means of selective visual stimulation various innate releasing mechanisms (catching of prey, flight response) were measured in field experiments with frogs (Rana esculenta). The results obtained with behavioral methods as well as the reactions of frogs to optokinetic stimulation (Birukow) were compared with the neurophysiological data from micro-electrode recordings of optic nerve fiber action potentials (Rana esculenta, Rana pipiens). The behavioral reactions are dependent on simple physical parameters of the visual stimuli (size, angular velocity, contrast). Certain features of the optical image on the retina are replicated by the discharge patterns of four different classes of ganglion cells. Each of these operations stresses somewhat different properties of the visual stimulus pattern. The activation of retinal neurons depends on angular velocity, contrast, angular size of the moving objects and their position in the receptive field. The constants of the functions valid for the four different classes of neurons differ significantly (Table 1). A comparison of the neurophysiological and the behavioral findings (Table 2) showed that visual stimulus patterns resulting in unequivocal behavioral reactions at the same time activate different classes of retinal neurons. It is thus shown that differentiation between behaviorally relevant key stimuli and behaviorally irrelevant stimulation requires an additional neuronal network in the optic tectum. The coding of the visual stimulation into the discharge patterns of the 4 different neuronal classes, however, exhibits retinal filter mechanisms which may be interpreted as the first step of the innate release mechanism. © 1968 Springer-Verlag.