Prefrontal cortex pyramidal cell morphology

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True   Likely   Speculative
Human Uniqueness Compared to "Great Apes": 
Speculative Difference
Human Universality: 
Individual Universal (All Individuals Everywhere)
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 Pyramidal cell morphology in the prefrontal cortex may be specialized in humans. A cross-species comparison of pyramidal morphology in layer III of a human, macaque, marmoset, baboon, vervet monkey, owl monkey, and galago in three separate cortical areas, primary V1, primary V2, and the dorsolateral PFC (DLPFC), found that the dendritic branches of the DLPFC were both more spinous and more complex compared to the primary visual areas in all species. However, they also found that the dendrites of the pyramidal neurons in the human specimen, which had the largest DLPFC of the individuals analyzed, were disproportionately more spinous than the primary visual areas, as well as disproportionately more spinous than the DLPFC of other species (human DLPFC was 70% more spinous than the macaque). These findings suggest that the human DLPFC receives significantly more excitatory inputs than does the corresponding area in other primates, and could be a feature of more complex connectivity in humans that supports the complex cognitive functions of the human PFC (Elston et al. 2006).
Another study examined dendritic branching of layer III pyramidal neurons in chimpanzees and humans in prefrontal area 10, primary somatosensory area 3b, primary motor area 4, and prestriate visual area 18, and found that dendritic branching is more complex in prefrontal area 10 compared to chimpanzees. However, they also found that human pyramidal neurons had more complex dendritic branching across all regions studied, but that this was not disproportionately increased in the PFC in humans (Bianchi et al. 2012).

Timing

Timing of appearance of the difference in the Hominin Lineage as a defined date or a lineage separation event. The point in time associated with lineage separation events may change in the future as the scientific community agrees upon better time estimates. Lineage separation events are defined in 2017 as:

  • the Last Common Ancestor (LCA) of humans and old world monkeys was 25,000 - 30,000 thousand (25 - 30 million) years ago
  • the Last Common Ancestor (LCA) of humans and chimpanzees was 6,000 - 8,000 thousand (6 - 8 million) years ago
  • the emergence of the genus Homo was 2,000 thousand (2 million) years ago
  • the Last Common Ancestor (LCA) of humans and neanderthals was 500 thousand years ago
  • the common ancestor of modern humans was 100 - 300 thousand years ago

Probable Appearance: 
2,000 thousand years ago
Definite Appearance: 
200 thousand years ago
Background Information: 

 Pyramidal neurons are by far the most abundant neurons in the cortex, comprising 70-90% of the total neuronal population (Elston et al. 2006). Pyramidal neurons are distinguished by a large apical dendrite and two basal dendrites that form dendritic trees that can become very complex. These neurons make up almost all cortico-cortical connections, as well as the majority of cortico-subcortical connections, and serve as both the main source and target of excitatory synapses. Subtypes of pyramidal neurons are identified by their morphological structure, and particularly the morphological structure of their dendritic trees; differences can be seen across species, brain regions, and even cortical layers. It is hypothesized that morphological specialization of pyramidal cells strongly influences cortical function (Elston et al. 2006; Elston 2007; Elston 2011; Petanjek et al. 2011).

The Human Difference: 

Spine densities of pyramidal cell dendrites are significantly more dense in the human PFC compared to the ape PFC.

Universality in Human Populations: 

 These findings are thought to be similar across all human populations.

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References

  1. Dendritic morphology of pyramidal neurons in the chimpanzee neocortex: regional specializations and comparison to humans., Bianchi, S., Stimpson C. D., Bauernfeind A. L., Schapiro S. J., Baze W. B., McArthur M. J., Bronson E., Hopkins W. D., Semendeferi K., Jacobs B., et al. , Cereb Cortex, 10/2013, Volume 23, Issue 10, p.2429-36, (2013)
  2. Pyramidal cells in prefrontal cortex of primates: marked differences in neuronal structure among species., Elston, Guy N., Benavides-Piccione Ruth, Elston Alejandra, Manger Paul R., and Defelipe Javier , Front Neuroanat, 2011, Volume 5, p.2, (2011)
  3. Specializations of the granular prefrontal cortex of primates: implications for cognitive processing., Elston, G. N., Benavides-Piccione R., Elston A., Zietsch B., DeFelipe J., Manger P., Casagrande V., and Kaas J. H. , Anat Rec A Discov Mol Cell Evol Biol, 01/2006, Volume 288, Issue 1, p.26-35, (2006)