No relative expansion of the number of prefrontal neurons in primate and human evolution

Abstract

Human evolution is widely thought to have involved a particular expansion of prefrontal cortex. This popular notion has recently been challenged, although controversies remain. Here we show that the prefrontal region of both human and nonhuman primates holds about 8% of cortical neurons, with no clear difference across humans and other primates in the distribution of cortical neurons or white matter cells along the anteroposterior axis. Further, we find that the volumes of human prefrontal gray and white matter match the expected volumes for the number of neurons in the gray matter and for the number of other cells in the white matter compared with other primate species. These results indicate that prefrontal cortical expansion in human evolution happened along the same allometric trajectory as for other primate species, without modification of the distribution of neurons across its surface or of the volume of the underlying white matter. We thus propose that the most distinctive feature of the human prefrontal cortex is its absolute number of neurons, not its relative volume.cortical expansion | evolution | number of neurons | primate | prefrontal cortex

A comparative neurological approach to emotional expressions in primate vocalizations

“…Compared with other primate brains, human brains have larger neocortices with more numerous cerebral gyri and deeper sulci, their temporal and frontal lobes contain more white matter, and their prefrontal cortices are characterized by higher white matter volume and gyrification (Rilling, 2014). However, human prefrontal cortices may not have undergone specific expansion compared to other primates apart from in absolute number of neurons (Gabi et al, 2016). Diffusion-weighted imaging or diffusion tensor imaging allows researchers to measure the diffusion of water molecules in the brain and to reconstruct major white-matter fibre tracts (Rilling et al, 2008).…”

Parkinson's disease: Is it a consequence of human brain evolution?

“…3 Expansion of the prefrontal cortex has been examined in detail, but there is ongoing debate on mechanistic aspects. 4,5 In comparison to other primates, molecular and cellular reorganization of neural circuitries in humans may be crucial. 6 The relative growth of the human cerebral cortex may have been attributed to relaxed genetic control and the shift in the human diet from exclusively plants to a mixture of plants and nutritionally dense animal tissue, which allowed the metabolic demands of the cerebral cortex to be met without expanding the digestive tract.…”

Genetics of Cerebellar and Neocortical Expansion in Anthropoid Primates: A Comparative Approach

“…The importance of the cerebellum in primate brain evolution is further bolstered by comparative analyses that demonstrate the cerebellum is expanded in hominoids [Rilling and Insel, 1998;MacLeod et al, 2003] due to a non-allometric expansion of the cerebellum relative to neocortex size that was caused by a faster-than-expected increase in cerebellum volume and neuron number that persisted throughout hominoid evolution [Barton and Venditti, 2014]. Although data at increasingly fine grained levels are more limited, the volumetric expansion of the whole cerebellum appears to be driven by a specific increase in the cerebellar lateral hemispheres [MacLeod et al, 2003] and possibly specific areas which receive direct functional connections with the prefrontal cortex [Balsters et al, 2010], an area of the neocortex long thought to be selectively expanded in hominoids [e.g., Semendeferi et al, 2001;Schoenemann et al, 2005;Sherwood et al, 2005;Smaers et al, 2011, but see Barton and Venditti, 2013;Gabi et al, 2016]. These data are indicative of an adaptive specialisation in the cortico-cerebellar functional relationship during hominoid evolution.…”