To heal hearing, try temporary blindness?
The link between blindness and musicianship is so strong that a legion of American blues singers adopted “Blind” as a nickname: Blind Willie McTell. Blind Boy Williamson. Many blind musicians reached the pinnacle of their fields. Pianist Art Tatum, for example, or singer Stevie Wonder.
Scientists have known that the brain regions that normally support the lost sense of vision can be press-ganged into serving a surviving sense, like hearing.
Musicians who were blind from birth, or at a young age, are renowned for awesome memory of songs and perfect pitch.
Age matters. Early in life, during the “critical period,” the brain has astounding ability to make changes and connections that are necessary for many types of learning. Afterwards, not so much.
Now we learn about hearing improvements in mice that, having left the critical period, lived one week in darkness. To document the effects, scientists measured changes in connections between different parts of the brain needed for hearing.
We asked corresponding author Patrick Kanold, a professor of biology at the University of Maryland, if he’d been listening to Ray Charles or Art Tatum, but he told us the study originated in curiosity about how the brain changes over time. “Dr. [Hey-Kyoung] Lee, my co-author, has been studying plasticity in the visual cortex for many years and I have been studying the auditory and visual cortex. We sat down together and thought, ‘What actually happens to the auditory cortex when you visually deprive an animal?’”
Neuroscientists use “plasticity” to refer to changes in the brain as a result of training or experience.
Understanding the impact of blindness was one goal of the study, he points out. “We know the blind hear much better, but what are the nuts and bolts? What changes?”
By recording electrical activity in the brains of mice, the researchers monitored connections, called synapses, between the thalamus and the cortex — an essential transition point for auditory impulses moving from the ears deep into the brain, where they are interpreted as sound. As the synapses between the thalamus and cortex change, “the flow of information into the auditory cortex is increased,” Kanold says.
Specifically, the experimental mice became able to distinguish among different pitches, between pure tones of 8,000 hertz and 8,050 hertz. “Neurons in the normal mice can’t discriminate that, but the dark-raised mice can distinguish it; and they are also more sensitive to soft stimuli,” says Kanold.
The exact mechanism is unclear, Kanold says, but it may involve either or both of these explanations:
When vision is turned off, neurons in the visual cortex are starved for input, “so they decide to up-regulate the input of auditory information”; and/or
an animal living in the dark pays more attention to auditory stimuli, “and we know that when you pay more attention, you improve your sensory performance.”
In any case, when the lights are turned on after a week, the auditory response returns to its original status, Kanold says. “It’s possible if we keep them in the dark longer, that could make the auditory change more permanent.”
Help on the way?
Finding flexibility in the brain of a mature mouse just by turning off the lights for a week is significant. Could a technique based on temporarily restricting vision help people who have difficulty understanding speech in a noisy restaurant, locating the source of a sound or enjoying music?
“I don’t think there is a system in place to do this,” says co-author Amal Isaiah, a senior resident in ear, nose and throat medicine at the University of Maryland. “There was some data to suggest the brain’s ability to change with training, but there was never a fixed paradigm, such as blindfolding, that would lead to so much increase in auditory acuity.”
If seven days of darkness can improve hearing in the mice, Isaiah wonders about people. “Our work has brought some hope that a fixed duration of visual training can improve auditory performance.” In the past, he says, people have been deterred by the need for a long period of darkness, “but this is not that long, you might need a blindfold for x number of hours; not weeks or months.”
Not blind to the consequences
Although we began with the extraordinary auditory abilities of blind musicians, the present study shows a related but different phenomenon. In blind people, visual areas of the brain begin to serve other functions, Kanold says. “When they read Braille, the visual cortex is active. We find hearing function is improved” because the auditory cortex has been altered by changes in the visual realm.
Finding so much plasticity in “adult” mice (defined as older than the critical period) was “a big surprise,” he says. “The brain is much more changeable in circumstances where we thought it could not change.”
And that suggests a possible end-run on rehabilitation, he says. Many therapies are focused on the system that is deficient, “but maybe that’s not the best way.” Maybe it’s possible to “open some space” in the brain by changing a different sensory system, he says.
– David J. Tenenbaum
Terry Devitt, editor; S.V. Medaris, designer/illustrator; Yilang Peng, project assistant; David J. Tenenbaum, feature writer; Amy Toburen, content development executive
- Cross-modal induction of thalamocortical potentiation leads to enhanced information processing in the auditory cortex, Emily Petrus et al, Neuron, 6 February 2014. ↩
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- Why Can Some Blind People Process Speech Far Faster Than Sighted Persons? ↩
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- Top 10 Blind Male Musicians ↩