People who are born blind may use the part of the brain associated with vision to process language, say US scientists.
A new study led by neuroscientists from the Massachusetts Institute of Technology (MIT) shows how the brain adapts to early blindness.
"Brain regions that are thought to have evolved for vision can take on language processing as a result of early experience," the researchers write in the Proceedings of the National Academy.
The ability to speak and understand language is primarily associated with two specialised centres in our brains Ч Broca's area located in the left-hand side of the brain's frontal lobe, and Wernicke's area, located in the brain's temporal lobe.
Studies in the past have also shown that people who've been blind since birth also use the visual cortex located in the brain's occipital lobe during verbal tasks such as reading Braille, and have good verbal long-term memory.
But it was unclear if the visual cortex processed complex language such as sentences in the same way as the classic language regions in the brain.
To test whether the visual cortex could take on more complex language tasks, the researchers scanned the brains of 22 sighted people and 10 people who were blind from birth or an early age while they listened to a brief verbal passage. The group then answered questions about the passage.
They then scanned another group of 17 sighted people and 11 people who were blind at birth while they listened to different sounds such as sentences, a list of words, a 'jabberwocky' sentence (a sentence containing nonsense words) and a list of non-words.
The researchers found that the left visual cortex of the blind participants was active during sentence comprehension, even when the tasks were more demanding.
"The idea that these brain regions could go from vision to language is just crazy," says Dr Marina Bedny from MIT.
"It suggests that the intrinsic function of a brain area is constrained only loosely, and that experience can have a really a big impact on the function of a piece of brain tissue."
This doesn't mean, however, that the traditional language centres in the brain are redundant, says Bedny.
"We haven't shown that every possible part of language can be supported by [the visual cortex]. It just suggests that a part of the brain can participate in language processing without having evolved to do so."