PROJECTIONS FROM THE VISUAL AREAS TO THE NEOSTRIATUM IN RATS - A REEXAMINATION

Neostriatal afferents from the primary visual cortex in rats were stud ied using dextran-biotin, biocytin, and Fluoro-Gold. The area V1 was f ound to project only to a dorsomedial, longitudinal region of neostria tum (NS), bordering on the lateral ventricle and subcortical white mat ter. The preterminal fibres in the NS form fluffs which increase in nu mber and density in the cases with larger injections. This target regi on is poorly stained for calbindin and yet belongs to the matrix compa rtment. The secondary visual areas also project to the dorsomedial NS region but they also innervate the deeper tissue in the same general r egion. Iontophoresis of Fluoro-Gold into the dorsomedial NS labelled s ome pyramidal neurones in the fifth layer of the primary visual cortex . The cortical areas that surround the visual cortical complex project to other regions of the NS: the somatosensory cortex to a dorsolatera l longitudinal region and the auditory area to the medial half of the caudalmost portion of NS. Thus, major sensory cortical divisions proje ct to non-overlapping NS regions. Since NS in monkeys and cats does no t receive afferents from the primary visual cortex and in a number of other species does, we conclude that visual systems in different mamma ls differ with respect to their projections to NS.