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Connectivity of language areas Unique in the human brain

Overview: Researchers shed new light on how the human brain evolved to be ready for language. Compared to the brains of chimpanzees, the connection patterns of language areas in the human brain expanded more than previously thought.

Source: Radboud University

Neuroscientists have gained new insight into how our brains evolved into a language-ready brain. Compared to the brains of chimpanzees, the connection pattern of language areas in our brains is more extensive than previously thought.

The researchers from Radboud University and the University of Oxford will publish their findings in PNAS on 4 July.

“At first glance, the brains of humans and chimpanzees are very similar. The mind-boggling difference between them and us is that we humans communicate with language, while non-human primates don’t,” said co-first author Joanna Sierpowska.

Understanding what in the brain made this unique ability possible has inspired researchers for years. Until now, however, their attention has mainly been drawn to a particular nerve tract connecting frontal and temporal lobes, the arcuate fasciculus, which are known not only to show significant differences between species but also to be involved in language function.

“We wanted to shift our focus to the connectivity of two cortical areas in the temporal lobe, which are equally important to our ability to use language,” Sierpowska says.

To study the differences between the human and chimpanzee brains, the researchers used scans of 50 human brains and 29 chimpanzee brains that had been scanned in the same way as humans, but under well-controlled anesthesia and as part of their routine veterinary checkups.

More specifically, they used a technique called diffusion-weighted imaging (DWI), which images white matter, the nerve pathways that connect brain regions.

Using these images, they examined the connectivity of two language-related brain hubs (the anterior and posterior mid regions of the temporal lobe), and compared them between species.

“In humans, both areas are considered crucial for language learning, use and understanding and harbor numerous white matter pathways,” Sierpowska says.

“It is also known that damage to these brain regions has adverse effects on language function. But until now, the question of whether their pattern of connections is unique to humans has remained unanswered.”

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The researchers found that while the connectivity of the posterior midtemporal regions in chimpanzees is mainly limited to the temporal lobe, in humans a new connection to the frontal and parietal lobes arose using the arcuate fasciculus as an anatomical pathway. In fact, changes in both human language areas involve a series of extensions of connectivity within the temporal lobes.

This shows a woman's head
In fact, changes in both human language areas involve a series of extensions of connectivity within the temporal lobes. Image is in the public domain

“The results of our study imply that the arcuate fasciculus is certainly not the only driver of evolutionary changes that prepare the brain for a full-fledged language capacity,” said study co-author Vitoria Piai.

“Our findings are purely anatomical, so it’s difficult to say anything about brain function in this context,” says Piai.

“But the fact that this pattern of connections is so unique to us humans suggests that it may be a crucial aspect of brain organization that enables our distinctive language skills.”

About this language and evolutionary neuroscience research news

Author: Harriette Koop
Source: Radboud University
Contact: Harriette Koop – Radboud University
Image: The image is in the public domain

Original research: The findings appear in PNAS

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