Читать книгу The Behavior of Animals - Группа авторов - Страница 51

Prey-selective T5.2-neurons send their axons from the optic tectum to the medullary premotor/motor cells that innervate jaw and tongue muscles (Weerasuriya & Ewert 1981, Satou & Ewert 1983; cit. Ewert 1984; see also Table 2.6).

Table 2.6 Minimum number of cell types linking photoreception and snapping reaction. Additional interacting cells (e.g., retinal horizontal and amacrine cells; pretectal/thalamic neurons) have tuning and specifying functions at different processing levels.

Such a neuron can be examined by recording its activity with an electrode chronically implanted in the tectum of a freely moving toad in response to a prey-like stripe: a strong burst of impulses preceded toad’s tongue-projection at prey (Schürg-Pfeiffer et al. 1993). The same stripe presented in threat configuration elicited little neuronal activity and no prey-catching, probably due to pretectal/thalamic inhibition (see Figure 2.10B).

Test: If a second electrode—fastened at the skull—delivered an electrolytic lesion to the ipsilateral pretectal thalamus, a moving stripe strongly activated the prey-selective T5.2 neuron and elicited prey-capture regardless of whether the stripe was presented in prey or threat configuration. Pretectal/thalamic lesion (Figure 2.10D) impaired the discrimination between prey and threat both neuronally and behaviorally—hence evidencing linkage between prey-selective neuronal activity and prey-catching behavior (Schürg-Pfeiffer et al. 1993).

No motor command can be issued when motivation and attention are not appropriate: if a toad was satiated after feeding on mealworms or frightened by some noise by the experimenter, a prey object neither activated T5.2 neurons nor any prey capture.