Abstract
To study the relationship of the intralaminar nuclei to both cortex and striatum, degenerative changes in the brains of 39 monkeys (Macaca mulatta) were followed using the method of Nauta. Stereotactic lesions were placed in either the caudate nucleus or putamen in 26 animals, in the thalamus of three animals and in various parts of the cortex in the remaining 10 animals. After lesions of the frontal lobe, the rostral intralaminar nuclei show cell shrinkage and pallor but little to no cell loss. Lesions of the striatum and the internal capsule result in complete cellular degeneration of these nuclei. Lesions confined to the caudate nucleus produced no degeneration in the intralaminar nuclei. Localized lesions of the putamen produced slight cell shrinkage in the centromedian nucleus. Fibers from the cortex of the frontal lobe project to the intralaminar nuclei in large number and in a topographic-ally organized manner. Due to the relative insensitivity of cellular degeneration techniques and to the wide range of cellular reactions that are possible when axons are sectioned or deprived of their afferents, it still is not possible to locate the precise site of mode of termination of the efferent fibers of the intralaminar nuclei of the thalamus. Each of the intralaminar nuclei projects widely, in an organized manner upon both parts of the striatum. Axon collaterals to the cortex roust be considered. The cellular changes in the intralaminar nuclei after cortical lesions, however, may be adequately accounted for by transneuronal effects following removal of cortical afferents to these nuclei.