THALAMIC AND CORTICAL PROJECTIONS TO MIDDLE SUPRASYLVIAN CORTEX OF CATS - CONSTANCY AND VARIATION

We investigated the constancy and variability in the numbers of thalam ic and cortical neurons projecting to cat middle suprasylvian (MS) vis ual cortex. Retrograde pathway tracers were injected at a single anato mically and physiologically defined locus in MS cortex. Counts of labe led neurons showed that the visual thalamic projections to MS cortex c onsistently arose from a fixed set of nuclei in relatively constant pr oportions. In contrast, counts of cortical neurons revealed that trans cortical inputs to MS cortex were much more variable. This differentia l variability may be linked to the developmental program, which afford s greater influence of experiential factors on cortical pathway develo pment than on thalamocortical pathway development. These results have implications for the development of models of cerebral connectivity th at include measures of pathway variability.