New York, March 24: A new study has identified a feature unique to the human brain that is shedding light on how human language evolved.

The study, by researchers at Emory University, is the first to use diffusion tensor imaging (DTI), a non-invasive imaging technique, to compare the human brain to those of chimpanzees, our closest living relative.

To explore the evolution of human language, researcher James Rilling studied the arcuate fasciculus, a pathway that connects brain regions known to be involved in human language, such as Broca's area in the frontal lobe and Wernicke's area in the temporal lobe.

Using DTI, Rilling compared the size and trajectory of the arcuate fasciculus in humans, rhesus macaques and chimpanzees.

"The human arcuate fasiculus differed from that of the rhesus macaques and chimpanzees in having a much larger and more widespread projection to areas in the middle temporal lobe," said Rilling.

Findings of the study have been published in the online version of the journal Nature Neuroscience.

Previous studies have shown that the middle temporal lobe is involved with analysing the meanings of words. In humans, it seems the brain not only evolved larger language regions but also a network of fibres to connect those regions, which supports humans' superior language capabilities.

"This is a landmark," said co-author Todd Preuss.

"Until DTI was developed, scientists lacked non-invasive methods to study brain connectivity directly. We couldn't study the connections of the human brain, nor determine how humans resemble or differ from other animals.

"DTI now makes it possible to understand how evolution changed the wiring of the human brain to enable us to think, act and speak like humans."

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