Читать книгу The Behavior of Animals - Группа авторов - Страница 47

In leopard frogs, Rana pipiens, Barlow (1953) and Lettvin et al. (1959) recorded spike activities of retinal ganglion cells—from axon terminals in the optic tectum—toward objects traversing the center of a cell’s visual receptive field, RF (Figure 2.9A). The four classes of retinal ganglion cells differ in sensitivities to dimming/brightening, and to an object’s contrast, velocity, and size. The latter is correlated with the diameter of the excitatory RF ranging among different cell classes from 2 to 16 degrees visual angle.

Figure 2.9 Neuroimaging toad’s visual system. (A) Dorsal view of toad’s brain. A stimulus (S) traverses the receptive field (RF) of a retinal ganglion cell (G) of the right eye (E), whose optic nerve (ON) projects to left optic tectum (T) and pretectal thalamus (TH). R, receptor cells; DT, dorsal tectal lobe; VT, ventral tectal lobe; MP, telencephalic ventro-medial pallium; M, medulla oblongata. (B) Functional neuroimaging: ¹⁴C-2DG-uptake in brain transverse sections at levels a-d. (see also Suggested Reading, Movie A1). (a) After hand-conditioning of a right-eyed toad, left MP showed ¹⁴C-2DG-uptake toward the conditioned stimulus (Finkenstädt & Ewert 1988). (b) Toad escaping a predator stimulus showed strong ¹⁴C-2DG-uptake in DT and TH. (c) Toad stiffening toward a threat-like moving stripe presented to the right eye showed moderate ¹⁴C-2DG-uptake in left TH and less so in DT. (d) Toad binocularly snapping toward a prey-like stripe showed strong ¹⁴C-2DG-uptake bilaterally in VT (Finkenstädt et al. 1985.).

The pioneering work by Barlow and Lettvin and coworkers made us realize that retinal ganglion cells—the output neurons of the retinal network—perform a first-stage analysis of visual input. Subsequent quantitative investigations, however, showed that retinal processing is not sufficient to recognize prey, as suggested formerly. Applying the configurational stimulus paradigm, no correlation was found between retinal neuronal and prey-catching activities in common toads (Ewert & Hock 1972; cit. Ewert 1984). Consequently, configurational feature analysis requires further processing by retina-recipient neurons in the brain.