Neural Mechanism of Prey-catching Behavior in Anurans

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The optic tectum is a major visual center in lower vertebrates. It has been considered that in anurans visual informations, such as motion of prey-objects, are detected in the optic tectum, and 'motor-commands' for prey-catching behavior are sent out from there. On the other hand, we have shown that neuronal pathways from the optic tectum to the tongue-muscle motoneurons, which control the final phase of prey-catching behavior (the tongue-flipping movement), are composed of polysynaptic excitatory and inhibitory pathways (Satou et al. 1984, 1985).The present research aimed to (1) clarify how the prey-objects are detected by neurons in the optic tectum, and (2) identify interneurons intervened between the optic tectum and the tongue-muscle motoneurons. The results showed that (1) many neurons in the toad's optic tectum show a property of 'local motion detectors' which are activated selectively not by 'global motion', but by 'local motion' within the animal's visual field. It was proposed that these tectal 'local motion detectors' are involved in process of detection of prey-objects. (2) Furthermore, we showed that neurons in the re ticular formation, which receive inputs from the optic tectum and project to the hypoglossal and spinal motoneuron pools, are likely candidates for inhibitory interneurons mentioned above.Thus, neural processes underlying the toad's prey-catching behavior, from detection mechanism of prey-objects at the sensory-side to synaptic pathways towards motoneurons at the motor-side, are now being clarified.