Temporary blindness 'helps hearing'
Published 05/02/2014 | 17:12
A week of temporary blindness may help to tune up your hearing - a phenomenon dubbed the "Ray Charles effect", scientists believe.
In tests, researchers found that keeping mice in the dark for several days rewired circuits in the brain and improved their hearing.
They expect humans to respond the same way because the neural wiring involved in both species is similar.
Legendary soul singer and pianist Ray Charles, who died in 2004, was completely blind from the age of seven.
The new research suggests lack of sight may have enhanced the hearing sensitivity of talented musicians such as Charles and fellow blind star Stevie Wonder.
Scientists in the US showed how neural connections in the brain that manage vision and hearing work together to support each sense. The findings, published in the journal Neuron, could lead to new ways of helping people with hearing loss and tinnitus, distressing "ringing" in the ears.
Dr Hey-Kyoung Lee, a leading member of the team from the Mind/Brain Institute at the Johns Hopkins University, 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.
"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."
In the study, healthy adult mice were placed in a darkened environment for six to eight days, to simulate blindness, while their brain activity and response to sound was monitored.
When the mice were reintroduced to the light their vision was unchanged, but they could hear better than before.
As the researchers played a series of one-note tones, neurons in the auditory cortex involved in hearing fired faster and more powerfully than normal. They were also more sensitive to quiet sounds and better at discriminating between different sounds.
"Our result would say that not having vision allows you to hear softer sounds and better discriminate pitch," said Dr Lee.
"If you ever had to hear a familiar piece of music with a loud background noise, you would have noticed that sometimes it seems the beat or the melody is different, because some of the notes are lost with the background. Our work would suggest that if you don't have vision you can now rescue these 'lost' notes to now appreciate the music as is."
In addition the mice developed more nerve connections, or synapses, between the thalamus - a part of the brain that acts as a "switchboard" for sensory information - and the auditory cortex.
The changes occurred in a brain region that is structured much the same way in most mammals.
"This makes me hopeful that we would see it in higher animals too," said co-author Dr Patrick Kanold, from the University of Maryland.
"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."
After returning to normal lighting conditions the mice reverted to their usual standard of hearing in a few weeks.
In the next phase of their five-year study, the scientists plan to look for ways to make the sensory improvements permanent and to expand their scope beyond changes to individual neurons.
Dr Ralph Holme, head of biomedical research at the charity Action on Hearing Loss, said: " With limited options for treating hearing loss and no cure, this is an important piece of research and a fascinating study that tells us more about how our sensory systems interact.
"By understanding the mechanisms at play it may be possible to develop training or pharmacological approaches to boost the brain's ability to process sound and help people who are hard of hearing.
"More research is now needed, to establish if these changes actually lead to better hearing in humans and in the real world."