Role of the optic tectum and general cortex in reptilian vision

Abstract

Optokinetic performance was measured in two groups of red-eared turtles; nex t, one group received bilateral ablation of the general cortex and the other received bilateral ablation of the optic tectum. After recovery, optokinetic performance was measured again. Cortical ablation had no effect, whereas tectal ablation brought about a deficit in responding in a 19stripe, but not in a 4-stripe drum. These results support the traditional view that the optic tectum is a major visual center in reptiles.

Behavioral Studies of Telencephalic Function in Reptiles

“…Neither cortical nor tectal ablations alone affected the frequence of optokinetic nystagmus (OKN), whereas combined lesions of cortex and tectum led to a significant reduction in this type of eye movement. The absence of cortical lesion effects on OKR was confirmed in a subsequent study (Hayes and Hertzler, 1967), leading these investigators to conclude that the dorsal cortex "is not of particular functional importance" (Hertzler, 1972), at least in the kinds of visual discrimination capabilities they tested. They point out, however, that the cortex may play some role in visual behavior since combined cortical-tectal lesions produced more severe deficits than did tectallesions alone.…”

“…It appears that destruction of this tissue does not impair the ability to learn or remember simple spatial (Morlock, 1972;Peterson, this chapter) or visual problems (Bass et al, 1973;Peterson, this chapter). Neither is dorsal cortex necessary for discrimination of color (Diebschlag, 1938) or brightness (Peterson, this chapter), for normal optokinetic or visual cliff behavior (Hertzler and Hayes, 1967;Hayes and Hertzler, 1967), or for certain types of pattern vision (Bass et al, 1973).…”

“…Some 30 years later, Hertzler and Hayes published a series of papers (Hertzler and Hayes and Hertzler, 1967;reviewed in Hertzler, 1972) which dealt with the role of dorsal cortex in visual discrimination behavior. The primary rationale for these experiments was the notion that reptile general cortex might represent a stage in the development of mammalian neocortex.…”

“…Behavioral tests following lesions of dorsal cortex-with or without adjoining (large-celled) medial cortex-indicate that this tissue is not necessary for color (Diebschlag, 1938), brightness (Peterson, this chapter), depth (Hertzler and Hayes, 1967), and pattern (i.e., stripe; Hertzler and Hayes and Hertzler, 1967;Bass et at., 1973) vision. These results are consistent with evidence from more informal observations (Morlock, 1972;Goldby, 1937;Peterson, this chapter;Bass et at., 1973;Tarr, 1977a) that dorsal-cortex-Iesioned animals show no apparent deficits in visually guided behavior either on the testing apparatus or in a more "natural" setting such as the home cage (including large enclosures which simulate the experimental animal's environment in the wild).…”

“…The authors (Hertzler and Hayes, 1967) also tested turtles (T. carolina and Pseudemys scripta) in an optokinetic drum. Neither cortical nor tectal ablations alone affected the frequence of optokinetic nystagmus (OKN), whereas combined lesions of cortex and tectum led to a significant reduction in this type of eye movement.…”