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Differences in cortical serotonergic innervation among humans, chimpanzees, and macaque monkeys: a comparative study
Mary Ann Raghanti1, Cheryl D Stimpson, Jennifer L Marcinkiewicz
1Department of Anthropology and School of Biomedical Sciences, Kent State University, Kent, OH 44242, USA. mraghant@kent.edu
Cerebral Cortex (New York, N.Y. : 1991)
|June 26, 2007
Summary
Human intellectual evolution may be linked to serotonin transmission changes in the brain. Humans and chimpanzees show distinct serotonin transporter- (SERT-) axon patterns in key cognitive areas compared to macaques.
Area of Science:
- Neuroscience
- Evolutionary Biology
- Primatology
Background:
- Human intellectual capacities evolved significantly.
- Serotonin is a neurotransmitter implicated in cognitive functions.
- Changes in serotonin supply to the frontal cortex are hypothesized to support cognitive evolution.
Purpose of the Study:
- To investigate if altered serotonin supply to the frontal cortex supported human intellectual evolution.
- To compare serotonergic innervation patterns across humans, chimpanzees, and macaques.
Main Methods:
- Quantitative comparative analyses of serotonin transporter-immunoreactive (SERT-ir) axons in the cerebral cortex.
- Immunohistochemical visualization of SERT-ir axons.
- Evaluation of cortical areas 9 and 32 (working memory, theory of mind) and primary motor cortex.
Main Results:
- No overall quantitative increase in serotonin innervation in humans.
- Region- and layer-specific differences in serotonergic innervation patterns were observed.
- Humans and chimpanzees showed higher SERT-ir axon density relative to neuron density in layers V/VI of areas 9 and 32 compared to macaques.
- Morphological specializations (axon coils) were found in humans and chimpanzees, but not macaques.
Conclusions:
- Cortical serotonergic transmission significantly reorganized in humans and chimpanzees.
- These reorganizations, including specialized axon coils, may indicate enhanced cortical plasticity in hominoids.
- Findings suggest a role for altered serotonergic pathways in the evolution of higher cognitive functions.
