Prefrontal cortex pyramidal cell morphology
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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).
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).
Spine densities of pyramidal cell dendrites are significantly more dense in the human PFC compared to the ape PFC.
These findings are thought to be similar across all human populations.
Dendritic morphology of pyramidal neurons in the chimpanzee neocortex: regional specializations and comparison to humans., , Cereb Cortex, 10/2013, Volume 23, Issue 10, p.2429-36, (2013)
Pyramidal cells in prefrontal cortex of primates: marked differences in neuronal structure among species., , Front Neuroanat, 2011, Volume 5, p.2, (2011)
Specializations of the granular prefrontal cortex of primates: implications for cognitive processing., , Anat Rec A Discov Mol Cell Evol Biol, 01/2006, Volume 288, Issue 1, p.26-35, (2006)