According to an MRI study, blind people really have a more sensitive hearing

A new study released on Monday suggests that losing sight early in life can lead to slight changes in brain circuits primarily responsible for hearing.

It is generally thought that being born blind or losing sight early in life can make hearing more sensitive. Blindness, especially if a person is born with or if it occurs early in life, can make hearing more sensitive. However, while studies have consistently shown that blind people appear to have more accurate hearing in some respects, we do not know how and where this increased ability actually manifests itself in the brain.

The authors of this latest study, published in the Journal of Neuroscience, say that theirs is one of the first to look into what happens in the auditory cortex of blind people.

"Previous studies have really focused on behavioral aspects, and we are one of the first to attempt to approach it in a more modeled approach," said lead author Kelly Chang, a researcher in vision and cognition at the University of Washington. Gizmodo.

They scanned the auditory cortex of people born blind or having developed blindness early in life (including some people with anophthalmia, a disease in which the eyes are completely absent) via MRI. They were also scanned during hearing tests allowing them to listen to pure sounds. These sounds were played at different frequencies and their brain activity in the auditory cortex was measured as they heard these sounds. Their results were then compared to a medium vision control group. Everyone involved had an average audience.

They found that the auditory cortex was similar in both groups, including its size. But there was a clear difference in one aspect of how blind and sighted people treated sound. In the blind, the auditory cortex seemed more sensitive to certain frequencies of sound played during the test, depending on the type of brain activity that the researchers saw during scans.

"Let's say you wanted to distinguish between a low frequency note and a high frequency note. For the visually impaired, it's quite easy to do because the notes are very far apart. But among blind people who are blind, probably because they can only rely on their auditory system, they are actually much better able to distinguish between very close frequencies, "Chang said.

Other research has suggested that brain neural connections can reorganize when a person becomes blind, especially in areas that usually treat sight. This is an example of the well-known plasticity of the brain. The authors wrote that the results provide "some of the first evidence in humans" that this compensation can occur in areas of the brain that are not directly affected by blindness.

"To see this reorganization in such a fundamental place is remarkable," she said.

The small sample size of the study (nine subjects in total with early blindness, five with anophthalmia) means that the team's findings are far from definitive. But even if they were, there are still some important questions to solve, according to the authors.

First, it is the question of what makes this compensation possible in the auditory cortex of the brain. Previous research, notably conducted by the Chang team, suggested that this type of change can only occur when someone becomes blind in his childhood and not in those who lose their sight in the night. ;adulthood. And perhaps it is not the loss of sight itself that causes this reorganization in the auditory cortex, but the need for the blind to focus more on certain sounds to navigate the world. Another thing that needs to be studied is how people who become blind early in life transform sounds and speech, complex noises that require more cooperation between different areas of the brain.

Future studies to address these issues, which Chang and others are working on, could examine what happens in the auditory cortex in temporarily blinded people. They could also look at people who became blind in adulthood, including those who had regained their sight to some extent.