Introducing the brain: our structural differences (Introduction)

by David Turell , Thursday, March 27, 2025, 15:14 (7 days ago) @ David Turell

Other primate brains are different:

https://www.sciencealert.com/new-study-identifies-unexpected-part-of-your-brain-thats-u...

"Our recent study may have brought us one step closer by taking a new approach – comparing the way brains are internally connected.

"We used publicly available MRI data of white matter, the fibres connecting parts of the brain's cortex. Communication between brain cells runs along these fibres. This costs energy and the mammalian brain is therefore relatively sparsely connected, concentrating communications down a few central pathways.

"The connections of each brain region tell us a lot about its functions. The set of connections of any brain region is so specific that brain regions have a unique connectivity fingerprint.

"In our study, we compared these connectivity fingerprints across the human, chimpanzee, and macaque monkey brain.

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"Much of the previous research on human brain uniqueness has focused on the prefrontal cortex, a group of areas at the front of our brain linked to complex thought and decision making. We indeed found that aspects of prefrontal cortex had a connectivity fingerprint in the human that we couldn't find in the other animals, particularly when we compared the human to the macaque monkey.

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"The feature driving this distinction was the arcuate fasciculus, a white matter tract connecting the frontal and temporal cortex and traditionally associated with processing language in humans. Most if not all primates have an arcuate fasciculus but it is much larger in human brains.

"However, we found that focusing solely on language may be too narrow. The brain areas that are connected via the arcuate fasciculus are also involved in other cognitive functions, such as integrating sensory information and processing complex social behaviour.

"Our study was the first to find the arcuate fasciculus is involved in these functions. This insight underscores the complexity of human brain evolution, suggesting that our advanced cognitive abilities arose not from a single change, as scientists thought, but through several, interrelated changes in brain connectivity.

"While the middle temporal arcuate fasciculus is a key player in language processing, we also found differences between the species in a region more at the back of the temporal cortex.

"This temporoparietal junction area is critical in processing information about others, such as understanding others' beliefs and intentions, a cornerstone of human social interaction.

"In humans, this brain area has much more extensive connections to other parts of the brain processing complex visual information, such as facial expressions and behavioural cues. This suggests that our brain is wired to handle more intricate social processing than those of our primate relatives. Our brain is wired up to be social.

"These findings challenge the idea of a single evolutionary event driving the
emergence of human intelligence. Instead, our study suggests brain evolution happened in steps. Our findings suggest changes in frontal cortex organisation occurred in apes, followed by changes in temporal cortex in the lineage leading to humans.

"Richard Owen was right about one thing. Our brains are different from those of other species – to an extent. We have a primate brain, but it's wired up to make us even more social than other primates, allowing us to communicate through spoken language."

Comment: finding this difference is not surprising. Connectivity is one form of complexification, another is an increased number of interconnected neurons. The human brain has more of both.