Despite the long evolutionary history of our species, humans have only been reading and writing for a few thousand years. New research shows that we may have ‘recycled’ a key region of the brain to help us understand the written word.
In tests on rhesus macaque monkeys, scientists have shown that a region called the inferior temporal (IT) cortex in the primate’s brain is able to provide the essential information we need to translate character letters into something more significant.
That neural behavior suggests that, instead of developing new areas of the brain specifically for reading, people may have repurposed the same brain region while developing the ability to recognize words as they were written – what is known as orthographic processing.
“This work has opened up a potential link between our rapidly evolving understanding of the neural mechanisms of visual processing and an important primate behavior – human reading,” says neuroscientist James DiCarlo of the Massachusetts Institute of Technology (MIT).
Inferior temporal cortex, like gyrus, in yellow. (Gray726 / Wikimedia Commons / Public Domain)
This idea of brain rewiring to process written words has been suggested earlier. DiCarlo and his colleagues have previously investigated the role of the IT cortex in responding to objects, including faces, using functional magnetic resonance imaging.
They were also able to build on previous studies by some of the same researchers, and saw how parts of the inferior temporal cortex become highly specialized tools for recognizing words once we learn how to read. At present, however, not much is known about how this works at the neural level.
In the new experiments, the researchers checked about 500 different neural sites with implanted electrodes, because the animals were shown around 2,000 words and non-words. That data was entered into a computer model called a linear classifier, which was then trained to use the measured activity to make an intelligent guess about the nature of each string of letters.
“The efficiency of this methodology is that you do not have to train animals to do anything,” says neuroscientist Rishi Rajalingham, of MIT. “What you do is just record these patterns of neural activity when you flash an image to the animal.”
The model showed that brain activity was in fact able to provide information that would be primate needed to perform orthographic tasks, including the interpretation of images to distinguish between words and non-words. In fact, the linear classification could use this neural output to tell that difference with an accuracy of about 70 percent, compared to a 2012 study of baboons training to do the same thing.
Non-human primates, including macaques, show much the same brain behavior and ways of working as we do, and research suggests that there is not much difference between how these monkeys look and how humans do. .
The study also supports the idea that humans took the evolved mechanisms of the inferior temporal cortex and then re-adapted them to make good sense of words and symbols – although more research will be needed to know for sure.
“These results show that the IT cortex of untrained primates can serve as a precursor to orthographic processing, suggesting that the acquisition of reading in humans requires the recycling of a brain network developed for other visual functions,” the researchers concluded.
The study was published in Nature communication.
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