Differential connections in the brains of New World and Old World monkeys

Abstract

The brain’s network for somatosensory processing in primates is greatly expanded compared to other mammals, consisting of multiple thalamic nuclei and cortical areas. In an effort to better understand the changes that arose during this expansion, we studied primate somatosensory organization by looking at the connections that underlie the processing of tactile information. We placed injections of neuroanatomical tracers into different body part representations in primary and non-primary somatosensory cortical areas to reveal the network of projections to cutaneously responsive areas in the brains of Old World and New World monkeys. Thus, we were able to reveal aspects of the organization of the somatosensory network in both Old World and New World monkeys. Our results provide support for a model of anterior parietal cortex (APC) organization where phylogenetic relationships explain differences in APC organization among non-primate mammals, prosimian primates, and anthropoid primates, rather than a model built on hand-use that adds a fourth category of APC organization that is unique to certain New World monkey species. Variations within the basic APC pattern that are seen in species in each of the non-mammalian, prosimian, and simian categories of APC organization reflect specializations related to structure and use of the peripheral body.