Brains Of Blind People Rewire Themselves To Sharpen Their Hearing

Similar to the origin story of the masked vigilante Daredevil, researchers have shown how the brains of people who are blind from a young age can "rewire" to sharpen their sense of hearing and compensate for their loss of vision.

This specific demonstration of brain plasticity, the ability of the brain to modify its connections to adapt to new circumstances, has been widely suggested before. For example, you may have seen videos of blind people clicking (effectively using echolocation) to orient themselves to their surroundings. However, this is one of the first times that researchers have been able to show these profound changes by looking at brain activity within the auditory cortex of blind people. 

Writing in the Journal of Neuroscience and Proceedings of the National Academy of Sciences, researchers led by the University of Washington (UW) used functional magnetic resonance imaging (fMRI) to examine activity in the auditory cortex of people who were born blind or became blind early in life, as well two subjects who had been blind from infancy until adulthood but had their sight restored by surgery in adulthood.

In the first study, they measured neural responses in the participants while they listened to a sequence of Morse code-like bleeps. The fMRI scans showed that the auditory cortex of the blind participants was more adept at picking up on subtle differences between the frequencies of the bleeps compared to the people with vision.

“We weren’t measuring how rapidly neurons fire, but rather how accurately populations of neurons represent information about sound,” said Kelly Chang, a graduate student in the UW Department of Psychology and lead author on the Journal of Neuroscience paper, said in a statement. 

“Our study shows that the brains of blind individuals are better able to represent frequencies,” added Chang. “This gives us an idea of what changes in the brain explain why blind people are better at picking out and identifying sounds in the environment.”

For the second study, they examined how the brains of blind people kept track of moving objects. Specifically, they were asked to listen to how the sound changed as the object moved closer or further away. Once again, the auditory cortex of the blind participants was notably more on-point.

Interestingly, the participants who used to be visually impaired, but now have relatively good vision, were also found to have enhanced auditory processing. The researchers say that this confirms the idea that brain plasticity happens early in development.

“This is the first study to show that blindness results in plasticity in the auditory cortex. This is important because this is an area of the brain that receives very similar auditory information in blind and sighted individuals," added Ione Fine, a UW professor of psychology. “But in blind individuals, more information needs to be extracted from sound – and this region seems to develop enhanced capacities as a result.

“This provides an elegant example of how the development of abilities within infant brains is influenced by the environment they grow up in.”