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The neural basis of prey detection, recognition, and orientation was studied in depth by Jörg-Peter Ewert in a series of experiments that made the toad visual system a model system in neuroethology (neural basis of natural behavior). He began by observing the natural prey catching behavior of the common European toad (''Bufo bufo''). Ewert’s work with toads yielded several important discoveries (Ewert 1974, 2004). In general, his research revealed the specific neural circuits for recognition of complex visual stimuli. Specifically, he identified two main regions of the brain, the tectum and the thalamic-pretectal region, that were responsible for discriminating prey from non-prey and revealed the neural pathways that connected them. Furthermore, he found that the neural mechanisms are plastic and adaptable to varying environments and conditions (Carew 2000; Zupanc 2004). ==Natural toad behavior== :''For additional information, see Amphibian nervous and sensory systems and Frog sight. The common toad responds to a moving insect or worm with a series of prey-catching reactions: (1) orienting towards prey, (2) stalking up to prey, (3) binocular fixation, (4) snapping, (5) swallowing and (6) mouth-wiping with forelimb (Ewert 1974). This series of movement constitutes a stimulus-response chain, where each reaction of the toad provides the stimulus constellation for the next response. First, if an object is recognized as prey and thus catches the toad’s attention, the toad will orient towards the stimulus by turning its body to face it. Then it approaches the prey, binocularly focusing intently on it. During the attack, it snaps at the object with its tongue or jaws and swallows it. Finally, it wipes its mouth with a forelimb. These actions constitute a series of well-defined behavioral patterns. One reason for this type of stimulus-response chain is that, unlike humans, toads do not have involuntary saccadic eye movements and they also cannot perform “tracking eye movements” (Ewert 1980). They must, therefore, depend on recognizing the stimulus before they respond. As a result they have developed a specific detection system that, for example, allows them to discriminate between edible prey and dangerous predators. The lack of saccadic eye movements forces the toad to hold its eyes in rigid positions. Therefore, it must decide whether the object is “prey” or “non-prey” before moving itself. If it orients towards an object, it must already have decided “prey” and then commits itself to snapping by reducing the thresholds for subsequent prey-catching responses. Even when the prey stimulus quickly disappeared after orienting, the aroused toad may sometimes complete the subsequent responses. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Vision in toads」の詳細全文を読む スポンサード リンク
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