Sublamination within the superficial gray layer of the squirrel monkey: an analysis of the tectopulvinar projection using anterograde and retrograde transport methods.

Anterograde and retrograde tracing methods have been used to analyze the cells of origin and the axonal distribution of the tectopulvinar projection in the squirrel monkey. Our most interesting finding is that tectopulvinar neurons occupy a cytoarchitecturally distinct sublamina of the stratum griseum superficiale (SGS) called the lower SGS (SGSL). The distinction between the SGSL and the upper SGS (SGSU) is further indicated by the findings of others that the SGSL receives different amounts of retinal and cortical input compared to the SGSU. Previous physiological studies have also shown that cells in the SGSL possess different response characteristics than those in the SGSU. Differences in cytoarchitecture, afferent and efferent connections, and physiological properties of the SGSL versus the SGSU indicate that sublaminae are the anatomical mechanism which enables different information channels to maintain some degree of autonomy within the SGS, and at the same time use the same topographic map within this layer.