We hear it over and over again: As people go blind, their other senses heighten. But there has been growing evidence that the brain is indeed far more plastic in its handling of information than was ever believed. This seems to be confirmed by a new study, which found that in blind people, parts of the brain usually associated with vision have been repurposed to process sound instead.
The research, currently in pre-print on bioRxiv, highlights this incredible flexibility within the neural circuits that make up the brain. They tested both blind people and sighted people by making them listen to three different recordings of human speech. The first clip was completely understandable, the second was slightly distorted but the words could still be discerned, while the third was altered beyond recognition.
The participants were then played the three different tracks while their brains were being mapped using magnetoencephalography (MEG), which records the magnetic fields produced by the brain in order to build up a picture of activity. While both groups of people obviously showed signs of brain activity in the auditory sections of the brain, the researchers found that in the brains of the blind people, there was clear activity in the visual cortex too.
This is not actually the first time researchers have found that regions of the brain can be repurposed in blind people in order to process sound. A study published in 2015, for example, reported how the visual lobes in the brains of blind children were used to decode noises.
What is new about this latest study, however, is the fact that the researchers were able to observe how the visual parts of the brain modulate their response when exposed to sound. As the scientists played the participants the speech recordings, the neurons in the visual cortex of the blind people seemed to fire in synch with that of the voices, but only when it was intelligible. This, they argue, shows that the visual part of the brain is being used to understand language.
The work clearly demonstrates the astonishing ability of the brain to adapt, but the researchers suspect that there is a limit. They think that while the processing of a new input can be altered, the underlying architecture of that region of the brain is unlikely to change.
It is hoped, however, that if scientists can understand the changes that do go on, it could lead to new treatments for blind people.
[H/T: New Scientist]