Abstract # 2383 Poster # 36:

Scheduled for Thursday, June 19, 2008 05:00 PM-07:00 PM: Session 4 (Ball Rooms A and B) Poster Presentation

Evolutionary changes in cortical neuromodulator innervation within the frontal cortex of humans, chimpanzees, and macaque monkeys

M. A. Raghanti1, C. C. Sherwood2, P. R. Hof3,5 and J. M. Erwin4
1Kent State University, Department of Anthropology and, School of Biomedical Sciences, Kent, OH 44242, USA, 2The George Washington University, Washington, D.C. 20052 USA, 3Mount Sinai School of Medicine, New York, NY 10029 USA, 4VA-MD Regional College of Veterinary Medicine, Virginia Tech, Blacksburg, VA 24060 USA, 5New York Consortium in Evolutionary Primatology, New York, NY, USA
     The roles of neuromodulators in cognition and neurodegenerative disorders suggest that humans may exhibit increased innervation relative to other primates in executive cortical areas that support human-specific intellectual capacities. We conducted quantitative analyses in humans (Homo sapiens), chimpanzees (Pan troglodytes), and macaques (Macaca maura) (n=6 each) of axons immunoreactive for dopamine, serotonin, and acetylcholine in prefrontal areas 9 (inductive reasoning) and 32 ("theory of mind"), with area 4 (primary motor cortex) as a control. Stereologic methods were employed to quantify the ratio of axon length density to neuron density in layers I, II, III, and V/VI for each neuromodulator. Data were analyzed using ANOVA and post-hoc tests for interaction effects [a=0.05]. Neuromodulator innervation was not uniformly greater in humans than in nonhumans, but humans and chimpanzees differed from macaques in having more serotonergic afferents in layers V/VI of areas 9 and 32; more dopaminergic input to layers III and V/VI of areas 9 and 32; and a pattern of cholinergic input that emphasized innervation to layers V/VI. No differences were detected in the control region. Morphological specializations that may represent localized cortical plasticity were observed for each neuromodulator in humans and chimpanzees, but not macaques. These results suggest significant evolutionary reorganization of prefrontal cortical neurotransmission in chimpanzees and humans that increased capacities for cognitive and behavioral flexibility.