Cerebral Sulci and Gyri Observed on Macaque Endocasts

Abstract

In order to evaluate the extent of the subdivisions of Neanderthal brains, we explored methods to determine the extent of subdivisions of brains in extant primate species. In the present study, we analyzed skulls and brains of macaque monkeys (Macaca fascicularis). Under deep anesthesia, five aged monkeys were perfused transcardially with phosphate-buffered 10 % formalin. The heads were scanned using a Toshiba Asterion CT scanner, and the reconstructed skulls and endocasts were compared with the convolutional patterns of the brain. In contrast to adult humans, which barely exhibit impressions in the upper part of the calvaria, the endocasts of the monkey skulls showed marked impressions of the cerebral sulci and gyri through the entire surface. On the dorsolateral surface, we identified most of the major sulci including the principal, arcuate, central, intraparietal, lunate, lateral, and superior temporal sulci, as well as the gyri in-between. On the ventral surface, we identified the medial and lateral orbital sulci, and the anterior middle temporal sulcus. Some of the individual differences in sulcal patterns were also observed on the endocast surface. We can thus infer the extent of major subdivisions of the macaque cerebral cortex by creating endocasts.