Anterograde degeneration study of the cortical projections of the lateral geniculate and pulvinar nuclei in the tree shrew (Tupaia glis)
Sixty lesions were placed in the pulvinar nucleus or the lateral geniculate nucleus of the tree shrew, and degenerated axons and their terminals were traced to the cortex. In all but two of the animals the electrode approached the thalamic target through the cerebellum and midbrain, thus sparing the cortex and thalamic nuclei other than the target nuclei. The results show that the pulvinar nucleus projects in a topographic fashion to an extensive cortical zone that includes areas 18, 19 and several temporal areas below 19. While there are several architectonic areas in its cortical target, no corresponding subdivisions could be established within the pulvinar nucleus, and its projections are best explained in terms of a single topographic organization. Further, since the pulvinar nucleus receives fibers from the superficial layers of the superior colliculus, its extensive cortical target can be regarded as primary visual cortex. The lateral geniculate nucleus projects in a precisely topographic fashion to area 17. Further, the evidence suggests that each layer of the lateral geniculate nucleus projects to a horizontal strip within the fourth or granular layer of area striata. With respect to the question of the relation between ocular dominance and location in area 17, the pattern of projections from the lateral geniculate nucleus does not reveal ocular dominance columns in layer IV of the tree shrew. In contrast to these results Hubel and Wiesel have shown that in the monkey there are vertical columns of cells in layer IV driven by either the homolateral or the contralateral eye. The case for the cat may be different from either of the other two species, thus posing the problem of discovering the mammalian plan and departures from the prototypical organization.
Harting, JK; Diamond, IT; Hall, WC
Journal of Comparative Neurology
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