Brain's 'Hearing Center' May Reorganize After Implant Of Cochlear Device

Brain's 'Hearing Center' May Reorganize After Implant Of Cochlear Device

Science Daily — Cochlear implants--electronic devices inserted surgically in the ear to allow deaf people to hear--may restore normal auditory pathways in the brain even after many years of deafness.
The results imply that the brain can reorganize sound processing centers or press into service latent ones based on sound stimulation. Jeanne Guiraud, PhD, and colleagues at the University of Lyon, Edouard Herriot University Hospital, and Advanced Bionics, a firm that makes cochlear implants, worked with deaf subjects from 16 to 74 years old and found that younger subjects and those with a shorter history of deafness showed changes that mirrored patterns in people with normal hearing more closely.
"The results imply a restoration to some extent of the normal organization through the use of the cochlear implant," says Manuel Don, PhD, of the House Ear Institute in Los Angeles. "They also claim to find ties between the degree of restored organization and a hearing task. Such ties are of enormous importance in evaluating cochlear implant benefits." Don was not involved in this study.
Guiraud and her team studied 13 profoundly deaf adults who had received cochlear implants, on average, eight months before the study. Electrical stimulation to the ear allowed the team to locate where in the brain's auditory cortex various frequencies were processed and come up with a map for these tones. Their results demonstrated that in people who had cochlear implants for at least three months, normal frequency organization was somewhat restored.
"Our results strongly suggest that the recipient's auditory cortex presents a tonotopic organization that resembles the frequency maps of normal-hearing subjects," says Guiraud.
In the future, the team hopes to determine in detail the ways in which these maps may change as a result of cochlear implants by studying subjects immediately following implant surgery.
The work was a supported by a grant from Advanced Bionics Europe. The results were published in the July 18 Journal of Neuroscience.
Note: This story has been adapted from a news release issued by Society for Neuroscience.



New bionic ear uses smart plastic
Judy Skatssoon
ABC Science Online


Tuesday, 12 April 2005
Hearing loss can cause cells in the ear to die
The bionic ear technology, which coaxes nerve cells to regrow, may also one day help to repair damaged spinal cords (Image: iStockphoto)
Scientists are building a new bionic ear coated in a smart plastic that boosts the growth of nerve cells in the inner ear when it's zapped with electricity.
The technology, which also has potential for healing spinal cord injuries, is being developed at the Australian Centre for Medical Bionics and Hearing Science, part of Melbourne's Bionic Ear Institute.
Collaborator, Professor Gordon Wallace of the Intelligent Polymer Research Institute at the University of Wollongong, says the polymer polypyrrole is unusual because unlike most plastics, it can conduct electricity.
It can also act as a host structure for the molecules that stimulate nerve regrowth, known as neurotrophins.
Passing a small electric current through the plastic releases the molecules and helps to reverse the death and degeneration of hearing cells that occurs after prolonged deafness.
"We can encompass these molecules in the polymer structure," Wallace says.
"We inject small amounts of electricity into the structure and that causes the release of the molecules and makes them available to the nerve cells.
"The polymer controls the timing of release, and where the molecules are released, to maximise interaction with nerve cells."
The device would be powered by a small battery.
Wallace says the cell regrowth will create a better connection between the brain and the device, improving hearing when there's a noisy background and making listening to music easier.
Other applications of polypyrrole including batteries, biosensors, artificial muscles and generating solar energy, he says.
Encouraging cells to grow back
Wallace says his team has already demonstrated in the lab that it's possible to incorporate a particular neurotrophin, NT3, into the polymer and stimulate its release.
Once released, NT3 induced damaged nerve cells to grow again, he says.
He says the next step for developing the new bionic ear is improving the structure of the plastic to ensure the growth factors are released within the right time frame and in the right amount.
"When this is ascertained it would be programmed into the material," he says.
A senior researcher at the bionics centre, which was officially opened by Prime Minister John Howard this week, says the technology is also being investigated for spinal cord repair.
Dr Adrian Cameron says a polymer-coated tube-shaped device loaded with growth factors could be implanted at the site of a spinal cord injury to help mend damaged nerve fibres, or axons.
"What we want to do is to reconnect the broken axons above the injury with the intact motor control centres below the injury," he says.
"We intend to use the polymer growth factor device as bridge."