The arcuate fasciculus is a bundle of nerve fibers and a main white matter pathway in the brain that connects the frontal, temporal, and parietal lobes. This nerve tract connects the middle temporal gyrus in human brains, and this connection is critical for understanding and producing language. It was once thought that the specific connection of the arcuate fasciculus to the middle temporal gyrus was unique to humans, but researchers from the Max Planck Institute for Human Cognitive and Brain Sciences found that chimpanzee brains also feature the same language-critical connection.
Humans Share the Same Arcuate Fasciculus Connection With Chimps: Chimpanzee Brains Reveal Evolutionary Roots of Language
Arcuate Fasciculus in Humans and Other Animals
The arcuate fasciculus is present in other primates. Non-primates also have similar white matter tracts that connect frontal and temporal brain regions but these are not called arcuate fasciculus. Nevertheless, when compared to other primates, the particular arcuate fasciculus in human brains is significantly different in size, connectivity, and lateralization.
Note that the unique characteristics of the human arcuate fasciculus are thought to be a critical component in the evolution of language. The expansion and specialization of this white matter tract, particularly its left-lateralized projections to specific temporal and frontal areas, are seen as crucial for the complex language abilities that are unique to humans.
The connection of the arcuate fasciculus to the middle temporal gyrus is also considered critical in the development of human language abilities. Scientists once thought that this connection was unique to humans. This assumption also supported the notion that human language abilities come from dedicated brain structures not found in other species.
Characteristics of Arcuate Fasciculus in Chimpanzees
Researchers from the Max Planck Institute for Human Cognitive and Brain Sciences retested the aforementioned assumption by investigating the brains of chimpanzees. Their exploration involved using high-resolution diffusion MRI scans of the brains of 20 chimpanzees who were either found in the wild or kept in captivity and later died of natural causes.
The high-resolution brain scans of post-mortem chimpanzee brains revealed that chimpanzees also have a direct arcuate fasciculus connection to the middle temporal gyrus. This exciting finding challenges the long-held assumption that the human arcuate fasciculus is unique. It also showcases that a critical brain connection for language exists in chimpanzees.
It is important to underscore the fact that the specific arcuate fasciculus connection to the middle temporal gyrus in chimpanzees is weaker compared to humans. This means that it is less developed as evident from fewer nerve fibers and thinner or shorter connections. The weaker connection also suggests that it is not as specialized as its human counterpart.
Implications for Evolution and Further Research
The study above suggests that language-related neural specialization in humans probably developed through a gradual evolutionary strengthening of a connection that already existed in our ancestors. It also argues that human language abilities did not arise de novo or emerge from scratch or on their own independent from external continuing evolutionary factors.
Moreover, based on the findings, the study also proposes the neutral architecture related to human language abilities was likely already present in the last common ancestor of chimpanzees and hominins or humans and their direct ancestors around 7 million years ago. This then enabled the evolution of language processes in the human lineage.
The research team headed by Alfred Anwander plans to continue their work by collaborating with wildlife reserves, sanctuaries, and zoos. Their goal is to correlate behavioral data from living great apes with their brain structures to further explore the neuronal foundations of cognitive abilities in these animals or to explore how these abilities relate to their brain wiring.
FURTHER READINGS AND REFERENCES
- Becker, Y., Eichner, C., Paquette, M., Bock, C., Girard-Buttoz, C., Jäger, C., Gräßle, T., Deschner, T., Amarasekaran, B., Asiimwe, C., Aschoff, D., Bleyer, M., Chantrey, J., Fedurek, P., Flores, K., Gone Bi, Z. B., Jaffe, J. E., Hambrech, S., … Anwander, A. 2025. “Long Arcuate Fascicle in Wild and Captive Chimpanzees as a Potential Structural Precursor of the Language Network.” Nature Communications. 16(1). DOI: 1038/s41467-025-59254-8
- Becker, Y., Loh, K. K., Coulon, O., and Meguerditchian, A. 2022. “The Arcuate Fasciculus and Language Origins: Disentangling Existing Conceptions that Influence Evolutionary Accounts.” Neuroscience & Biobehavioral Reviews. 134: 104490. DOI: 1016/j.neubiorev.2021.12.013
- Ivanova, M. V., Zhong, A., Turken, A., Baldo, J. V., and Dronkers, N. F. 2021. “Functional Contributions of the Arcuate Fasciculus to Language Processing.” Frontiers in Human Neuroscience. 15. DOI: 3389/fnhum.2021.672665