April 4, 1995
Media Contact: Beth Saverino or John Welby
Phone: (410) 955-1078
Listed below are hearing and balance story ideas from The Johns Hopkins Medical Institutions. To pursue any of these stories, call John Welby or Beth Saverino at (410) 955-1078.
DOES OUR BRAIN TELL OUR EARS WHAT TO HEAR?
When we hear, sound energy rushes along the auditory nerve, first to the brainstem, then up through several areas of the brain to the "highest" level -- the cortex. Now, Hopkins scientists have found evidence that this process also occurs in reverse. Signals originating in the cortex are rushing backward to the brainstem and may be influencing what we hear.
"It's like the brain is telling the ears what to hear," says David Ryugo, Ph.D., director of research in otolaryngology at Hopkins.
According to Ryugo, information traveling back to the auditory brainstem may be responsible for our ability to ignore background noise and focus on speech. Ryugo says understanding this direct link between the cortex and the auditory brainstem should lead to better hearing aids and listening devices.
COST-EFFECTIVE, LESS INVASIVE TECHNIQUE RESTORES BALANCE
Until now, one of the most effective treatments that doctors had to restore balance was an operation called labyrinthectomy. The treatment restores balance by completely disabling an inner ear's malfunctioning balance system, forcing the system in the unaffected ear to compensate. The success rate of this procedure is 95 percent.
Now, specialists at Johns Hopkins can achieve the same level of recovery without invasive surgery, says Lloyd Minor, M.D., of the Hopkins Center for Hearing and Balance. Using genomycine, a poison that shuts down key cells in the balance system, Minor disables the balance system in one ear, forcing the other ear to work harder.
The non-surgical treatment, now in clinical trials, is administered via injection into the ear once a week for four weeks. The technique preserves hearing while treating the balance disorder, and is cheaper than surgery.
CLOSE YOUR EYES, MISS THE ANSWER
When an inner ear infection makes you unsteady, dizzy and nauseated, the temptation is to lie down, close your eyes, and wait it out. But according to David Zee, M.D., professor of neurology at Johns Hopkins, "We should do exactly the opposite. This is precisely when we need stimulation both from our eyes and our feet. Our brain needs the experience of trying to walk and focus our eyes so it can begin the process of recovery."
According to Zee, our vestibular, or balance system, modifies signals sent to the brain based on the information it receives from the environment. When the balance system is temporarily compromised, it can develop coping strategies and eventually rehabilitate itself. Zee is studying how rehabilitation occurs in order to design new programs of therapy to hasten recovery.
WHERE SOUND COMES FROM
We hear a bell or a whistle and almost instantly we "fix" the source of the sound. But this apparently simple response is actually the result of a series of complex computations carried out by the brain, that would be impossible without the two highly visible flaps of cartilage we call ears.
Eric D. Young, Ph.D., professor of biomedical engineering, of neuroscience and of otolaryngology (head and neck surgery) at Johns Hopkins, has shown that our ability to localize sound is a completely different process from our ability to hear and is highly dependent on the external ear. Young says the shape of our ears, the distance of our ears from the sound source, and the distance between our two ears all play a part in the process. Understanding this process will help researchers design more sophisticated hearing aids that will help many of the 28 million Americans suffering from hearing loss.
BALANCE: AN OPEN AND SHUT CASE
Tilt your head, and immediately impulses from the eyes and the inner ear notify your brain to keep you "balanced." Yet after the brain takes in this information, it no longer needs to be told that your head is tilted.
The nervous system's ability to dampen or stop sending messages about a particular sensory event -- called adaptation -- keeps human and animal brains from being swamped and overwhelmed by information.
Hopkins neuroscientist Peter Gillespie, Ph.D., assistant professor of physiology, says this process is amazingly mechanical. Within the ear, tiny hairlike tufts found atop special sensory cells contain at their tips the biological equivalent of bottle caps. When gravity or other forces push the hairs over like so many tin soldiers, the "caps" pop open, allowing an incredibly fast flow of current to enter the cells. This starts the message to the brain about the new position. Working with frogs, Gillespie also has found an adaptation system that appears to ease the caps shut.