Study reveals a scientific basis for a link between blindness and improved hearing

 By David H. Kirkwood

COLLEGE PARK/BALTIMORE, MD–Stevie Wonder, Andrea Bocelli, Doc Watson, Ray Charles, Art Tatum, Ronnie Milsap, Sonny Terry, Blind Lemon Jefferson… The list of great singers and instrumentalists who were blind from birth or childhood goes on and on.

It’s often been theorized that their blindness may have been a factor in the development of their musical genius. Possibly, the brain compensated for sensory deprivation of one type by strengthening the auditory system and making their hearing exceptionally acute.

Alternatively, children whose blindness prevented them from pursuing activities such as painting, acting, or sports may have channeled their time and talents into pursuits, such as music, where vision is not essential. Or it may simply be that we pay more attention to a great performer’s blindness than we do to the normal vision that most famous musicians have. How memorable is it if Beyonce or Springsteen has 20-20 vision?

While the jury is still out on what effect blindness may have on a person’s hearing and ability as a musician, a fascinating study published this month in the peer-reviewed journal Neuron presents evidence that being deprived of sight can sharpen hearing in animals.

 

 

AFTER A WEEK IN THE DARK, MICE HEARD BETTER

Researchers from the University of Maryland in College Point and Johns Hopkins University in Baltimore simulated blindness in several adult mice with normal vision by placing them in complete darkness for six to eight days. After the mice were returned to a normal light-dark cycle, their vision was unchanged. However, the scientists found, the mice, which had previously had normal hearing, heard better than before their time in the dark.

In their experiment, the researchers played a series of one-note tones and tested the responses of individual neurons in the auditory cortex of the brain.

They found that in the mice that experienced simulated blindness the neurons in the part of the auditory cortex that receives signals from the thalamus fired faster and more powerfully when the tones were played, were more sensitive to quiet sounds, and could discriminate better among sounds. These mice also developed more neural connections between the thalamus and the auditory cortex.

The mice’s super hearing did not last long. Within a few weeks of their experience with simulated blindness, their hearing reverted to normal.

In the summary to their article in Neuron, the scientists wrote, “Sensory systems do not work in isolation; instead, they show interactions that are specifically uncovered during sensory loss… Here, we show that visual deprivation leads to improved frequency selectivity as well as increased frequency and intensity discrimination performance of A1 neurons… Our results suggest that adults retain the capability for cross-modal changes whereas such capability is absent within a sensory modality. Thus, multimodal training paradigms might be beneficial in sensory-processing disorders.”

 

ADULT BRAINS FOUND TO BE MALLEABLE

A significant aspect of the study was the finding that simulated blindness affected the brain circuitry in adult animals. It has been shown before that very young brains are malleable enough to re-wire some circuits that process sensory information. However, the finding that the adult mice in this research had that same ability was not necessarily anticipated.

 

IMPLICATIONS FOR PEOPLE?

The finding that a period of simulated blindness improved hearing mice raises the question of whether the same would be true for people, specifically for people with hearing loss.

Patrick Kanold, PhD, one of the two lead authors of the study, addressed the topic with Heather Dewar, a science writer at the University of Maryland College of Computer, Mathematical, and Natural Sciences. Kanold, an associate professor of biology who is an expert on how the brain processes sound, said, “There is some level of interconnectedness of the senses in the brain that we are revealing here.”

Hey-Kyoung Lee, PhD, the other lead author, said, “We can perhaps use this to benefit our efforts to recover a lost sense.” The associate professor of neuroscience and researcher at the Mind/Brain Institute at Johns Hopkins added, “By temporarily preventing vision, we may be able to engage the adult brain to change the circuit to better process sound.”

(Lee talks more about the research in a YouTube video with Three Blind Mice playing in the background.

Kanold and Lee also spoke about the implications of their study with Latarsha Gatlin of the Johns Hopkins Office of Communications and Public Affairs.

Kanold said that the fact that the changes in the mice occurred in the cortex, which is structured about the same way in most mammals, suggests that flexibility across the senses is a fundamental trait of mammals’ brains.

He continued, “This makes me hopeful that we would see it in higher animals too. We don’t know how many days a human would have to be in the dark to get this effect, and whether they would be willing to do that. But there might be a way to use multi-sensory training to correct some sensory processing problems in humans.”

Lee said, “In my opinion, the coolest aspect of our work is that the loss of one sense, vision, can augment the processing of the remaining sense, in this case, hearing, by altering the brain circuit, which is not easily done in adults.”

She added, “By temporarily preventing vision, we may be able to engage the adult brain to change the circuit to better process sound, which can be helpful for recovering sound perception in patients with cochlear implants for example.”

In the next phase of their 5-year study, Kanold and Lee will look for ways to make the sensory improvements permanent, and to look beyond individual neurons to study broader changes in the way the brain processes sounds.

The research received funding from the National Institutes of Health. The other investigators were Emily Petrus, David Li, and Hui Wang, all from Johns Hopkins University, and Adam P. Jones and Amal Isaiah from the University of Maryland.

For more on this subject, see my blog colleague Bob Traynor’s post at Hearing International.