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The caudate nucleus has an inhibitory role (3, 14) in the integrational function of the central nervous system. Electrophysiological and behavioral signs of inhibition might be produced by low frequency stimulation of the caudate and blocked by natural or artificial arousing stimuli (4). The inhibitory effects integrate into the basic neural processes of excitation and inhibition which interact with the impulses reaching the central nervous system trhough the various sensory modalities (5, 8), and especially the visual system (2, 15). Inhibitory electrographical responses in the electroencephalogram elicited by caudate stimulation (“caudate spindle”) are blocked by the stimulation of the visual system. Similar relationships were observed in the other electrophysiological parameters as well (1, 15).

Study of the morphological changes in the lateral geniculate nucleus (LGN) following bilateral deafferentation has been the subject of numerous studies (2, 8, 14, 15, 16, 17, 22, 23, 27). Fewer papers have dealt with unilateral deafferentation of the LGN by sectioning the optic tract and keeping the opposite side intact as a control (3, 6, 7, 35). The changes in the LGN after deafferentation are not only determined by the deafferentation procedures used but also by the age and species of the animals. When one eyelid is sutured in a young kitten, some of the geniculate cells, deprived of their normal visual input, grow to a lesser degree than normal (37, 38). The transneuronal cell atrophy that occurs in the dorsal LGN after removal of one eye is more rapid in young than in adult cats (12, 13, 21, 37, 38), and atrophic changes continue well beyond the time at which geniculate cell growth has stopped (14). The role of a binocular or translaminar competition in the production of the trans-neuronal atrophy has been emphasized only in very young animals (7, 14). In contrast, the comparative studies of the optic tract transection and eye enucleation, by Garey et al. (6, 7) suggested that even in adult cats there is some degree of cellular reaction present between the cells of the laminae. Total or partial deafferentation of the LGN in man (11) and monkeys (1, 31) produces severe degenerative changes with the disappearance of the nerve cells. In dogs and cats, the results obtained by various authors show considerable discrepancies. Klassovskij and Kosmarskaja (18) found in young dogs after a bilateral enucleation a disappearance of most cell elements in the LGN, while Figurina (4) performing the same operation found a slight loss of the cells, only in the proximal parts of that nucleus.