Simulating blindness for as little as a week appears to improve hearing.
Mice kept in complete darkness for that period of time experienced a circuitry change in the primary auditory cortex of the brain. That area processes sound and allows conscious perception of pitch and loudness.
“Our result would say that not having vision allows you to hear softer sounds and better discriminate pitch,” says Hey-Kyoung Lee, a neuroscientist at the Mind/Brain Institute at Johns Hopkins University.
“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,” Lee says.
Lee and biologist Patrick Kanold at the University of Maryland, College Park, co-wrote a paper on their research for the journal Neuron.
In the dark
“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,” Kanold says. “But there might be a way to use multi-sensory training to correct some sensory processing problems in humans.”
The findings may also be used to help those experiencing hearing loss regain more use of that sense.
“By temporarily preventing vision, we may be able to engage the adult brain to now change the circuit to better process sound, which can be helpful for recovering sound perception in patients with cochlear implants, for example,” Lee says.
Blind musicians Stevie Wonder and Ray Charles are often cited as examples of how lack of sight can enhance hearing. Scientists, however, did not fully understand just how that happened until now.
Kanold, Lee, and colleagues placed healthy adult mice in a darkened environment to simulate blindness for about a week and monitored their response to sounds. Those responses and the animals’ brain activity were compared with those of a second group of mice in a traditional, naturally lit environment.
The researchers concluded that a certain set of connectors in the primary sensory areas of the brain, called thalamocortical inputs, are less flexible later in life. When another sense is also impaired, however, those connectors can be reactivated to support the sense that is lagging.
The brain changes discovered by the researchers are reversible, meaning the mice that experienced simulated blindness reverted to normal hearing after a few weeks in a normal light-dark environment. In the next phase of their five-year study, Lee and Kanold plan to look for ways to make sensory improvements permanent. The pair also say they will look beyond individual neurons to study broader changes in the way the brain processes sounds.
The National Institutes of Health funded the study.