The Organization of the Cat Pretectum

Abstract

About ten years ago a number of investigators proposed that the mammalian visual system is composed of two divisions, one specialized in locating objects the other in identifying objects (1,2). According to this proposal, the geniculostriate system processes information about patterned stimuli while the superior colliculus allows the animal to orient in its visual world. This idea was based in part on an experiment done by SCHNEIDER, in which he showed that hamsters with lesions of the primary visual cortex are able to locate objects but fail pattern recognition tasks while hamsters with lesions of the superior colliculus can learn to recognize patterns but have difficulty in locating them (2). The concept of two visual systems was also based on anatomical studies which showed that the dorsal lateral geniculate nucleus and the superior colliculus are the two major targets of the retina in mammals. In this scheme other retinal targets are considered less important, partly because they are smaller and partly because there have been fewer studies of their function. More recently, however, an anatomical technique based on axoplasmic transport, the autoradiographic technique, has been developed (3, 4), and the central projections of the retina have been found to be much more widespread than previously thought. In the cat the retina projects to the dorsal lateral geniculate nucleus and to the superior colliculus, but following an injection of tritiated amino acids into an eye label can be seen in the following areas as well: the ventral lateral geniculate nucleus, the medial intralaminar nucleus: the suprachiasmatic nucleus of the hypothalamus; the dorsal, medial, and lateral nuclei of the accessory optic tract; the pulvinar, and two nuclei of the pretectal complex: the olivary pretectal nucleus and the nucleus of the optic tract (5, 6). If each of these retinal targets is considered a separate visual system, then there must be eleven visual systems. The pretectal complex receives a major retinal input, but among the way stations of the mammalian visual system, it has proved to be particularly refractory to functional interpretations. As a first step toward understanding the function(s) of the pretectal complex, I have studied its afferent and some of its efferent connections using anterograde and retrograde techniques.