Cytomorphology of the area striata in Saimiri sciureus. A Golgi study

Nissl- and Golgi preparations of the brain of the New World Monkey Saimiri sciureus were used to determine neuronal cell types and their distribution in the primary visual cortex (area striata or area 17). The visual cortex is located occipitally, mainly constituting the cortical surface around the calcarine fissure with six different laminae (total thickness about 1,300 micron). As the prevailing cell types, spiny neurons, such as pyramids and pyramid-like cells, many spiny multipolar cells, giant spine-free cells and a variety of bipolar-to-bitufted cells were detected. Shapes of pyramidal cells and their distribution resembled those of other primates. They were found in all laminae except LI and LIV, with large forms in LIII and LV. Non-pyramidal cells, however, showed deviating shapes and distribution patterns as compared with respective results in Old World Monkeys. Large spiny stellate cells were not only seen in lamina IV but also quite frequently in laminae II and III. Lamina V contained giant spine-free cells that have so far not been localized in area 17 of Old World Monkeys. The results imply that the differences in the functional organization of the area 17 between Old World Monkeys and New World Monkeys (Van Essen, 1979; Hendrickson, 1985), i.e. information processing with or without "ocular dominance columns", are also represented in the neuronal "hardware", that is, the cell types and their laminar organization and distribution.