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People who are blind use parts of their brain that normally handle for vision to process language, as well as sounds – highlighting the brain’s extraordinary ability to requisition unused real estate for new functions.
Neurons in the part of the brain normally responsible for vision synchronise their activity to the sounds of speech in blind people, says Olivier Collignon at the Catholic University of Louvain (UCL) in Belgium. “It’s a strong argument that the organisation of the language system… is not constrained by our genetic blueprint alone,” he says.
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The finding builds on previous research showing that the parts of the brain responsible for vision can learn to process other kinds of information, including touch and sound, in people who are blind.
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Collignon and his colleagues made the discovery using magnetoencephalography (MEG), which measures electrical activity in the brain.
While they were being scanned, groups of sighted and blind volunteers were played three clips from an audio book. One recording was clear and easy to understand; another was distorted but still intelligible; and the third was modified so as to be completely incomprehensible.
Both groups showed activity in the brain’s auditory cortex, a region that processes sounds, while listening to the clips. But the volunteers who were blind showed activity in the visual cortex, too.
The blind volunteers also appeared to have neurons in their visual cortex that fired in sync with speech in the recording – but only when the clip was intelligible. This suggests that these cells are vital for understanding language, says Collignon.
The right architecture
The visual cortex contains the relevant architecture, he says, to go from sound processing to language comprehension.
“The new finding is perhaps not surprising, but it is groundbreaking,” says Daniel-Robert Chebat at the Israeli Ariel University in the West Bank. “It shows that these parts of the brain are not only recruited [to receive new kinds of input], but can adapt and modulate their response.”
The discovery highlights how malleable our brains are, says Collignon, but he thinks there may be a limit to this. It’s unlikely that any part of the brain can eventually learn any function, he says. Instead, there may be a set of rules, laid down in our genes, which brain regions can follow.
Past research has found, for example, that a part of the visual cortex is responsible for tracking moving objects in sighted people. This same region seems to track the sound of moving objects in blind people.
There is also a visual aspect to understanding language, says Collignon. It is easier to understand what someone is saying if you are looking at them and watching the movements of their lips, for instance. “Brain regions are more dedicated to a function than to an input,” he says.
Collignon hopes his research will aid the development of treatments to restore vision. Several groups are currently working on bionic eyes and stem cell transplants, for instance. By better understanding how the brain can adapt to new inputs, researchers may be able to predict whether such treatments can rewire the recipient’s brain to allow them to see.
Journal reference: bioRxiv, DOI: 10.1101/186338
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