1Anthropology, Kent State University, 2School of Biomedical Sciences, Kent State University, 3Anthropology, The George Washington University, 4Neuroscience, Mount Sinai School of Medicine
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Cortical cholinergic innervation has been implicated in learning and memory functions. Additionally, variation in the density of cholinergic axons within the neocortex has been associated with inter-individual differences in learning abilities among rodents. Our earlier analyses revealed differences in cholinergic innervation within the frontal cortex among humans, chimpanzees, and macaques. To explore this finding further, the present study represents a large-scale comparative analysis of cholinergic innervation among a wide range of anthropoid primate species, including humans, chimpanzees, gorillas, baboons, moor macaques, pigtailed macaques, capuchins, and squirrel monkeys. Stereological methods were employed to obtain cholinergic axon length density to neuron density ratios (ALv/Nv) in layers III and V/VI of areas 44, 22, 10, and 24. The ratio of varicosity density, an additional measure of innervation, to neuron densities (Vv/Nv) was also quantified in layers III and V/VI of area 24 and area 44. In all layers and areas, Vv/Nv was significantly correlated with ALv/Nv. Results of a mixed-model ANOVA indicated significant differences in the densities and patterns of cholinergic innervation among species that did not follow a phylogenetic pattern. Post hoc analyses demonstrated that differences included significantly divergent patterns and densities of innervation between the two macaque species included in this analysis, but did not reveal a human-specific increase or alteration of cholinergic innervation within the cortical areas examined here. The results of the present comparative analysis, including a large number of primate species, demonstrate that human cognitive abilities are independent of a significant increase in cortical cholinergic innervation.
This research was funded by NSF BCS-0921079