In a nutshell: Humans are not the only primate species to have subdivisions in the frontopolar cortex.

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The ultimate aim of neuroscience is to understand the human brain. When experiments on humans are not possible, researchers rely instead on animal studies. But what can data from these species tell us about the evolution of the human brain?

The frontopolar cortex is a part of the brain found only in primates. In humans, it has subdivisions with different brain connectivity and functions. In non-human primates such as macaques and marmosets, however, no such subdivisions had been found – suggesting that humans were the only species to have undergone this evolutionary change.

Brain Function CoE chief investigator Marcello Rosa, associate investigator Sofia Bakola, and affiliate PhD student Tristan Chaplin from Monash University, in collaboration with researchers in Brazil, Poland and the USA, studied the connections that the frontopolar cortex makes to the rest of the brain in tufted capuchin monkeys.

The capuchin has a similar brain structure to the macaque, but is more closely related genetically to the marmoset. The three species also have different brain sizes: capuchin brains are ten times larger than the marmoset’s, but slightly smaller than the macaque’s.

The researchers found that brain size is related to the pattern of connections between brain areas: the smaller the brain, the more interconnected the areas become.

They also found that different parts of the frontopolar cortex in the capuchin monkey make distinctive connections with other areas of the brain, hinting at precursors of the subdivisions found in human brains (although these appear to be less distinct). These results suggest that the organisation of the brain’s surface is essentially similar across all primates, with the differences in connectivity determined mostly by the number of brain cells.

Next steps:
The researchers plan to perform imaging studies in humans, as well as comparative studies in other primates, to understand the exact functions of the frontopolar cortex subdivisions and how they affect the cognitive abilities of different animals.

Rosa, M. G. P., Soares, J. G. M., Chaplin, T. A., Majka, P., Bakola, S., Phillips, K. A., Reser, D. H., & Gattass, R. (2018). Cortical afferents of area 10 in Cebus monkeys: implications for the evolution of the frontal pole. Cerebral Cortex. doi: 10.1093/cercor/bhy044

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