THE LAMINAR PATTERN OF THE LATERAL GENICULATE BODY IN THE PRIMATES

In the past the lateral geniculate body has tended to receive less than its due share of attention in the investigation of the neural basis of vision. Yet a detailed study of the intermediate cell station in the lateral geniculate body is clearly an essential part of such an investigation. The anatomical situation of the nucleus renders it difficult of direct experimental approach, and our present knowledge of it still rests largely on elementary anatomical methods. The stratified structure of the lateral geniculate body is well known, and in the higher Primates it may consist of as many as six laminae. The termination of crossed and uncrossed optic nerve fibres in alternate lamine is also well established. Brouwer and Zeeman (1925, 1926) worked out a gross quadrantic projection of the retina in the nucleus by the application of the Marchi technique, and the details of this projection were further elucidated by Le Gros Clark and Penman (1934) by the study of transneuronal degeneration following small localized retinal lesions. Little, however, is yet known of the significance of the laminar disposition in different parts of the nucleus. Some misunderstanding in the past regarding the form and fofding of the geniculate lamine has evidently resulted from the difficulty of interpreting individual sections cut in different planes. For instance, in the human lateral geniculate body, a section in one plane gives the appearance of " inversion" of the lamine, with the large cell lamine forming the outermost layer, in another plane a pattern of "; eversion" may be seen, and in a third plane both eversion and inversion become evident. So, also, the number of laminx may appear to vary according to the plane in which the section is taken. Hence it becomes necessary to make reconstruction models so that the intranuclear differentiation and disposition of all the layers can be easily visualized. Thuma (1928) acdopted this method in his study of cat's lateral geniculate body, as also did Balado and Franke (1937) in their comprehensive work on the human geniculate body. Le Gros Clark did -the same for Macaca mulatta (1941). This method further clarifies the relation of the nucleus to the surrounding neural structures, and facilitates the mapping of the projection fields of the retina. The significance of changes in the laminar pattern in a phylogenetic series can also be studied. Above all it affords an opportunity for a comparative study of the anatomical basis of the binocular and monocular representation fields, the central and peripheral vision fields, and changes in the lateral geniculate body associated with incomplete or hemi-decussation of optic nerve fibres.