Scientists supported by the National Institute on Deafness and Other Communication Disorders (NIDCD), Bethesda, Md,one of the National Institutes of Health, will be presenting their latest research findings at the 2010 Midwinter Meeting of the Association for Research in Otolaryngology (ARO) on February 6 to 10 at the Disneyland Hotel, Anaheim, Calif.
Research topics to be presented by NIDCD-funded scientists will include:
Noise-Damaged Hair Cells Can Regrow Stereocilia in Mammals if Rescued in Time
Scientists have been trying to regenerate hair cells—sensory cells in the inner ear named for the hairlike bundles jutting from their tops—out of surrounding nonsensory cells as a way to make up for hair cell loss in ears damaged by noise, some medicines, and other sources. (Unlike other vertebrates, mammals aren’t able to grow new hair cells on their own once the cells are dead or damaged.) But new NIDCD-funded research from Creighton University, Neb, and the Chinese PLA General Hospital, Beijing, says that hair cells damaged by noise may have more life in them than we once thought. We may be able to regenerate new hair bundles—called stereocilia—from the original hair cells. The researchers subjected guinea pigs to an impulse noise simulating gunfire, resulting in severe hearing loss. Using scanning electron microscopy, they showed extensive stereocilia damage had occurred throughout the inner ear. However, when the researchers injected math1, a key gene for the development of hair cells, into the inner ear within 1 week of damage, they found that the stereocilia were able to grow back. Furthermore, key measurements showed that the new stereocilia were able to convert sound vibrations into electrical signals, which is how the brain interprets sound. The researchers caution that there is a window of time when the hair cells are still viable following noise damage. If the hair cells are not rescued within that time frame, they will die. But if researchers are able to intervene early enough—within 10 days—the hair cells can possibly be saved. The researchers plan to conduct tissue culture studies to confirm whether these findings are supported at the cellular level.
The talk “Regeneration of Stereocilia of Cochlear Hair Cells by Math1 Gene Therapy”(#484) takes place Sunday, February 7, at 5 pm PT in the Disneyland South Ballroom.
Success of Second Cochlear Implant Depends on Age at Which Child Receives First Implant
The cochlear implant has been a highly successful biomedical technology for the treatment of severe to profound hearing loss in children. Parents of children who wear a cochlear implant face the question of whether two implants would be better than one. However, the success rate of the second implant has varied across studies, and researchers haven’t understood why. In new NIDCD-funded research from the University of Colorado at Boulder, Arizona State University, and the Rocky Mountain Ear Center, scientists have found that the age at which a child receives his or her first implant is extremely important in determining whether the second implant will be effective. They studied 38 children, all of whom received their first cochlear implant by 3½ years of age, and who received their second implant between the ages of 1 and 17 years. Measuring neural activity in the auditory cortex, the hearing center of the brain, the researchers found that children who received their first implant under age 1½ years responded well to the second implant, even if they received the second implant as late as 9 years of age. Conversely, virtually all children who received their first implant at 2½ years or later did not respond as well to the later second implant, regardless of when they received it. These results were backed up by studies of how well the participants understood speech in both quiet and noisy conditions. The researchers plan to investigate a possible mechanism underlying their findings by incorporating brain imaging technology to determine if early implantation stimulates both sides of the brain, while later implantation activates only one side.
The poster "A Sensitive Period for Cortical Development and Plasticity in Children with Sequential Bilateral Cochlear Implants" (#897) takes place Monday, February 8, at 1 pm PT in the Disneyland Exhibit Hall.
A Dinner Party Dilemma: How Does Your Brain Sift through the Sounds of Too Many Talkers?
If you’re trying to follow one dinner party conversation amid a lot of background chatter, your brain cells are doing the same thing. NIDCD-supported researchers have found that when you are in an environment where there are many competing sounds, nerve cells in the auditory cortex—the part of the brain that interprets the sounds you hear—divide up the listening duties so that one population of neurons will focus on one sound source and another population will focus on the second source. In research conducted by the University of California, Irvine, University of Michigan, and University of Western Ontario, study participants who were surrounded by loudspeakers were asked to identify a rhythmic pattern played from one sound source when it was played at the same time as a competing pattern. Not surprisingly, they found that the participants had a tough time telling the patterns apart when they came from the same speaker. But when the sources of the sounds were spaced a very small distance apart from each other—as little as 5 10°—they had no problem identifying the sound patterns. In addition, in a similar study with cats, the researchers recorded neural activity in the auditory cortex when competing sounds were played. They found that when the sounds came from the same speaker, auditory neurons were synchronized to the combined sounds, but when the sources were separated by 5 to 10°, one group of neurons became synchronized to one sound while another population of neurons became synchronized to the second sound.
The talk "Independent Neural Populations Embody Perceptually Discrete Auditory Streams" (#471) takes place Sunday, February 7, at 4:15 pm PT in the Disneyland Center and North Ballroom.
Moderate Hearing Loss at an Early Age Can Have Long-lasting Effects on the Brain
Researchers have known for some time that severe hearing loss caused by damage to the inner ear can alter the connections between nerve cells in the auditory cortex, a part of the brain that processes sound. However, it was not clear whether moderate forms of hearing loss caused similar changes to the brain, and whether the neural connections remained altered as the brain developed or they continued to mature until they reached a normal adult state. In a new study from New York University, researchers asked if a moderate form of hearing loss, similar to that caused by ear infections or abnormalities in the middle ear, could alter the function of auditory cortex connections and, if so, whether these changes persisted into adulthood. The research team induced moderate hearing loss in young gerbils by removing one of the middle ear bones from each ear. They then waited one week for some animals to develop and allowed others to reach adulthood. When the researchers examined the neural connections in the auditory cortex, they found that those in the adult cortex were just as impaired after two additional months of development as they had been shortly after the hearing loss began. The researchers’ next step will be to learn what happens if the animal’s hearing ability is returned after 2 to 3 weeks. They hope to find out if a short period of moderate hearing loss early on—much like a childhood ear infection—has a similar long-term effect on the function of neural connections in the brain.
The poster "Conductive Hearing Loss Produces Changes in Cortical Inhibition That Persist to Adulthood" (#814) takes place Monday, February 8, at 1 pm PT in the Disneyland Exhibit Hall.
Inner Ear Antiviral Holds Promise for Preventing Cytomegalovirus-related Hearing Loss
Cytomegalovirus (CMV) is a widespread infection that is harmless for most people. But if a mother passes it to her unborn child, serious health problems can result, including hearing loss, and disorders of the brain, bone marrow, liver, or spleen. Researchers estimate that up to 20 percent of childhood hearing loss is caused by CMV infection. In other studies of children with CMV, researchers had found that antivirals given intravenously can improve hearing, though they can result in serious health complications. Researchers at the University of Cincinnati and the Cincinnati Children’s Hospital Medical Center are working to develop a safer, more effective way to treat CMV-infected children with hearing loss by restricting the drug treatment to the inner ear. They infected the inner ears of guinea pigs with CMV and found the guinea pigs indeed had developed hearing loss. They then delivered the antiviral drugs ganciclovir and cidofovir into the ear and found that the virus had not only stopped replicating, but the guinea pigs’ hearing had improved. In addition to testing a liquid form of the antiviral, the researchers are experimenting with a temperature-sensitive material that changes from liquid to gel when subjected to body temperature. The gel could be engineered to break down quickly and rapidly release the drug, or to remain for a longer time for a sustained delivery of medication. In 2012, the researchers plan to implement a clinical trial of CMV-infected children with hearing loss to see if treating them with antiviral therapies in the inner ear will help protect their hearing.
The poster "Intratympanic Delivery of Antivirals and the Effects on SNHL" (#655) takes place Monday, February 8, at 1 pm PT in the Disneyland Exhibit Hall.
Growing an Ear Where No Ear Has Grown Before
Deep inside the inner ear, two types of nerve pathways shuttle their messages to and from the brain. Afferent nerves carry messages from the ear to the brain about the sounds your ear hears as well as balance information. Efferent nerves carry information from the brain back to the inner ear to help the ear make necessary adjustments. Researchers have known that the efferent nerves in the inner ear are modified motor neurons that have evolved from neurons that innervate muscles in the face. NIDCD-funded researchers from the University of Iowa wanted to know if other motor neurons in the body could be rerouted to innervate the ear if it were placed in their way. Using tadpoles of an aquatic frog (Xenopus laevis), the researchers transplanted the tadpole ears into the tadpole’s upper side (trunk) or eye region and then watched what happened. They noticed that out of 109 transplanted ears, 73 developed with necessary inner ear structures, including sensory cells, called hair cells, which connect to the nerve fibers. Using a dye that labels only motor neurons, they first found spinal motor neurons had populated the ears in the tadpole’s trunk and cranial motor neurons had populated the ears in the eye region. Next, using antibodies, they demonstrated that connections were indeed forming between the efferent nerves and the hair cells. Finally, using electron microscopy, they showed that structures associated with afferent and efferent nerves were both present in the transplanted ear. Because the afferent nerves travel to the brain directly from the eye region or indirectly from the trunk region by way of the spinal cord, the researchers now want to find out what happens if the inner ear information travels to a non-auditory part of the brain and how that information will be processed.
The poster "Transplantation of Xenopus Laevis Ears Reveals Ubiquitous Rerouting of Motor Neurons to Become Efferents" (#552) takes place Monday, February 8, at 1 pm PT in the Disneyland Exhibit Hall.