title: Evolution of increased glia-neuron ratios in the human frontal cortex.
abstract: Evidence from comparative studies of gene expression and evolution suggest that human neocortical neurons may be characterized by unusually high levels of energy metabolism. The current study examined whether there is a disproportionate increase in glial cell density in the human frontal cortex in comparison with other anthropoid primate species (New World monkeys, Old World monkeys, and hominoids) to support greater metabolic demands. Among 18 species of anthropoids, humans displayed the greatest departure from allometric scaling expectations for the density of glia relative to neurons in layer II/III of dorsolateral prefrontal cortex (area 9L). However, the human glia-neuron ratio in this prefrontal region did not differ significantly from allometric predictions based on brain size. Further analyses of glia-neuron ratios across frontal areas 4, 9L, 32, and 44 in a sample of humans, chimpanzees, and macaque monkeys showed that regions involved in specialized human cognitive functions, such as "theory of mind" (area 32) and language (area 44) have not evolved differentially higher requirements for metabolic support. Taken together, these findings suggest that greater metabolic consumption of human neocortical neurons relates to the energetic costs of maintaining expansive dendritic arbors and long-range projecting axons in the context of an enlarged brain.
authors.affiliation: Department of Anthropology, The George Washington University, Washington, DC 20052, USA. sherwood@gwu.edu
authors.forename: Chet C
authors.initials: CC
authors.lastname: Sherwood
authors.forename: Cheryl D
authors.initials: CD
authors.lastname: Stimpson
authors.forename: Mary Ann
authors.initials: MA
authors.lastname: Raghanti
authors.forename: Derek E
authors.initials: DE
authors.lastname: Wildman
authors.forename: Monica
authors.initials: M
authors.lastname: Uddin
authors.forename: Lawrence I
authors.initials: LI
authors.lastname: Grossman
authors.forename: Morris
authors.initials: M
authors.lastname: Goodman
authors.forename: John C
authors.initials: JC
authors.lastname: Redmond
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Bonar
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Erwin
authors.forename: Patrick R
authors.initials: PR
authors.lastname: Hof
mesh_terms: D000818:Animals; D005075:Biological Evolution; D001921:Brain / Q000033:anatomy & histology* / Q000166:cytology; D002452:Cell Count; D005625:Frontal Lobe / Q000166:cytology* / Q000378:metabolism; D006801:Humans; D008251:Macaca / Q000033:anatomy & histology; D009457:Neuroglia / Q000166:cytology*; D009474:Neurons / Q000166:cytology*; D009929:Organ Size; D002679:Pan troglodytes / Q000033:anatomy & histology