title: Evolution of specialized pyramidal neurons in primate visual and motor cortex.
abstract: The neocortex of primates contains several distinct neuron subtypes. Among these, Betz cells of primary motor cortex and Meynert cells of primary visual cortex are of particular interest for their potential role in specialized sensorimotor adaptations of primates. Betz cells are involved in setting muscle tone prior to fine motor output and Meynert cells participate in the processing of visual motion. We measured the soma volumes of Betz cells, Meynert cells, and adjacent infragranular pyramidal neurons in 23 species of primate and two species of non-primate mammal (Tupaia glis and Pteropus poliocephalus) using unbiased stereological techniques to examine their allometric scaling relationships and socioecological correlations. Results show that Betz somata become proportionally larger with increases in body weight, brain weight, and encephalization whereas Meynert somata remain a constant proportion larger than other visual pyramidal cells. Phylogenetic variance in the volumetric scaling of these neuronal subtypes might be related to species-specific adaptations. Enlargement of Meynert cells in terrestrial anthropoids living in open habitats, for example, might serve as an anatomical substrate for predator detection. Modification of the connectional and physiological properties of these neurons could constitute an important evolutionary mode for species-specific adaptation.
authors.affiliation: Department of Anthropology, Columbia University, New York, NY, USA.
authors.forename: Chet C
authors.initials: CC
authors.lastname: Sherwood
authors.forename: Paula W H
authors.initials: PW
authors.lastname: Lee
authors.forename: Claie-Bénédicte
authors.initials: CB
authors.lastname: Rivara
authors.forename: Ralph L
authors.initials: RL
authors.lastname: Holloway
authors.forename: Emmanuel P E
authors.initials: EP
authors.lastname: Gilissen
authors.forename: Robert M T
authors.initials: RM
authors.lastname: Simmons
authors.forename: Atiya
authors.initials: A
authors.lastname: Hakeem
authors.forename: John M
authors.initials: JM
authors.lastname: Allman
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Erwin
authors.forename: Patrick R
authors.initials: PR
authors.lastname: Hof
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D005075:Biological Evolution; D002685:Chiroptera; D006801:Humans; D009044:Motor Cortex / Q000033:anatomy & histology* / Q000166:cytology*; D009474:Neurons / Q000166:cytology; D011323:Primates; D017966:Pyramidal Cells / Q000166:cytology*; D014417:Tupaia; D014793:Visual Cortex / Q000033:anatomy & histology* / Q000166:cytology*