Processing of area dimensions of visual key stimuli by tectal neurons inSalamandra salamandra

Summary

InSalamandra salamandra prey-catching behavior was investigated quantitatively in response to moving visual stimuli with the following Gestalt parameters: squares (S), worm-like (W), and antiworm-like (A) stripes of different sizes. It can be shown that the worm vs. antiworm preference is invariant irrespective of changes of the stimulus angular velocity, which contradicts earlier claims made by Luthardt and Roth (1979).

The activity of 47 tectal neurons in response to the same changing Gestalt parameters was recorded extracellularly and investigated quantitatively. Various classes of monocularly driven neurons can be distinguished according to their different ERF sizes; they correspond to large field class T2 neurons (ERF≃100 °), and T4 neurons (ERF≧ 100 °), and to small field T5 neurons (ERF≃34 °) described earlier in frogs and toads.

If the configurational (W, A) response properties of tectal neurons are considered, further (sub-)-classifications can be made with regard to worm preference (1), antiworm preference (3), and selective responses to large areas (4). Whereas class T5(1), T2(3), and T5(3) neurons have also been recorded from the tectum of toads and frogs, class T4(4) and T5(4) neurons appear to be unique toS. salamandra. In the fire salamander, class T5(1) neurons may fulfill functions of command elements in a system that generates the appropriate motor pattern of the prey-catching sequence. Class T5(4) and T4(4) neurons, on the other hand, are suitable candidates for command elements in another system that generates escape behavior.

No class T5(2) neurons have been identified inS. salamandra. It is suggested that highly selective class T5(2) neurons in anurans have evolved concurrently with the parcellation of the dorsal thalamus.