The neocortex has been both the theoretical and the experimental focal point of evolutionary studies dedicated to identifying unique features of the human brain; however, the neocortex is only one element of a neural network underlying human intellectual abilities. It is directly connected to and dependent upon other subcortical structures, especially the basal ganglia. Traditionally, the basal ganglia were known to regulate motor functions. Recently, however, they have been revealed to be active in advanced cognition, and their regulation of prefrontal cortical activity demonstrates that they are as important as the neocortex in processes such as language, learning, and memory. The goal of the present research is to examine the role of the basal ganglia in human cognitive development by comparing metabolic and modulatory components across a wide range of primate species, including humans and our closest living relative, the chimpanzee. The methods will combine advanced stereology with immunohistochemistry in order to quantify neuron to glia ratios, neuromodulatory neurons, and neuromodulator axons within key basal ganglia areas. This study will provide new knowledge about these subcortical structures, including any reorganization that may have occurred during human evolution. This will help distinguish our basal ganglia from those of other primates, promote understanding of how they changed during primate evolution, and how phylogenetic differences may relate to cognitive processing.
The research also may contribute substantially to understanding the etiology of major neuropathologies, such as Huntington's and Parkinson's diseases, by identifying how humans differ from other species in the basal ganglia regions most affected by these diseases. Histological sections and slides of many primate species will be generated, archived, and made available to other researchers for additional comparative studies. This work also will provide training for graduate and undergraduate students, including those enrolled in the McNair Scholars Program, which prepares individuals from under-represented groups for doctoral study.
