Our human brains are bigger than those of our ape relatives, in particular the frontal lobes that are required for advanced cognitive functions. Semendeferi et al have focused on a particular area of the frontal lobes: Brodmann area 10 (BA 10), which sits at the pole of the frontal lobes just above the eyes, and is thought to be involved in abstract thinking and other sophisticated cognition. They find not only that this area is relatively larger in humans, but that there is more space between nerve cell bodies in human brains than in the brains of apes, allowing room for connections between neurons. (In contrast, there were only subtle differences in cell body density among humans, chimpanzees, bonobos, gorillas, orangutans, and gibbons in the visual, somatosensory, and motor cortices.) Their analysis looked at the cells in layer three of the cortex, which communicates with other areas of the brain. BA10 in humans also contain a higher concentration of so-called Von Economo neurons, which are generally thought to be high-performance neurons specialized for rapidly transmitting information from one brain region to another.
More space between neurons in the human brain (right) compared with the chimp brain (left) could allow more complex neural wiring.
The authors suggest that human brain evolution was likely characterized by an increase in the number and width of cortical minicolumns and the space available for interconnectivity between neurons in the frontal lobe, especially the prefrontal cortex.