Topographic organization of certain tectal afferent and efferent connections can develop normally in the absence of...

To test the hypothesis that the topographic organization of the connections of the optic tectum is determined during development by the "retinotopically" ordered input that it receives from the eye, we have mapped certain of the connections of the tectum in chicken embryos and chicks in which both eye rudiments were removed before the outgrowth of optic fibers. Because several of the connections of the tectum are normally organized retinotopically, we should expect, if this hypothesis were correct, that some or all of these connectional patterns would be significantly altered in such "eyeless" chickens. In fact, we have found that the connections formed between the optic tectum and two of the isthmic nuclei, with which it is reciprocally connected, show the same topographic organization in "eyeless" animals as in control chickens raised under the same conditions. This clearly indicates that the topographic organization of the chicken optic tectum is independently specified and is not contingent upon the input that it receives from the retina.