The Cortical Projection upon the Claustrum.

Comparatively little is known about the connexions of the claustrum; two recent reviews (Rae, 1954; Berke, 1960) have summarized the evidence available from studies of normal and Marchi-stained material, and have emphasized the inadequacy of our understanding of the basic organization of the connexions of the claustrum. In view of the paucity of knowledge it was considered worthwhile to place on record the following observations on the cortical afferents to the claustrum derived from a large series of rabbit brains in which a variety of cortical lesions had been placed, prepared by the Nauta and Glees methods. The material was originally collected for a study of cor+,ostriate connexions, and from it 26 experiments have been selected for the present investigation. Several of these brains have been described previously, and the details regarding the placement of the lesions and the histological preparation have been given in full elsewhere (Carman, Cowan, and Powell, 1963). In each case the site and extent of the cortical lesion has been carefully reconstructed and transferred to a standard diagram of the rabbit hemisphere. The distribution of the fibre degenera-tion in the claustrum is similarly shown on a standard series of drawings from the projected outlines of a normal brain. To determine the basic organization of the projection of the cortex upon the claustrum it is convenient to divide the hemisphere into five topographic regions, and in the following account only one or two examples from each of these regions will be described. Experiment R48 is typical of several similar cases with lesions on the dorso-lateral aspect of the hemisphere and serves to illustrate many of the characteristic features of the cortico-claustral projection. The site and extent of the lesion are shown in Fig. 1; the area of cortical damage is roughly oval in outline and occupies the central part of the posterior half of the hemisphere immediately lateral to the 'cingular sulcus'. Throughout the greater part of its extent it has penetrated deeply into the white matter but has not involved the hippocampus. In continuity with the lesion severe fibre degeneration can be traced downwards and laterally in the corona radiata to the dorsal end of the claustrum. Here it separates into two components , the medial of which passes into the external capsule, and the lateral into the subcortical white matter on the outer aspect of the claustrum. From both components degenerating fibres can be …