As Donald Caspary has gotten older, he finds when he drives that he needs to adjust the volume of his car radio more often to offset the sound of the wind and the engine.
Caspary, 61, may not be losing his hearing, but his brain may have become less nimble in screening out background noise. It’s a common situation that requires him and many other drivers to reach for the volume knob on the radio for a better listening experience.
“Your brain used to do that for you very efficiently,” he said.
An internationally known neuroscientist at the Southern Illinois University School of Medicine, Caspary has worked with colleagues at SIU for the past 25 years to discover the chemistry that takes place in the brain as hearing ability declines with age.
The changes that cause inconveniences for drivers such as Caspary also contribute to the devastating loss of hearing that affects 30 percent of Americans 65 to 74 and at least half of Americans 75 and older.
SIU is one of a handful of academic centers in the United States with a team of scientists examining hearing loss in ways that could lead to drug treatments for people as they age and give them options beyond hearing aids.
“People don’t drop dead from hearing loss,” said Caspary, a professor of pharmacology at SIU. But he said hearing loss, which often causes people to withdraw socially, is a huge problem.
“It may be the second major malady after arthritic diseases in terms of raw numbers,” he said. “The only other one that comes close is hypertension.”
Caspary, a native of New York City, joined the medical school faculty in 1973 and has received more than $4.2 million in grant funding since then, mostly from the National Institutes of Health in Bethesda, Md.
He is part of SIU’s “auditory research group” — scientists who have received grants totaling $14.5 million since 1978.
Over the years, the scientists have deciphered part of the complex pathway that sound takes as it flows from the outer ear to the middle-ear bones, and then from the cochlea to nerve cells that fire off messages to various parts of the brain.
The researchers have begun to determine through studies on laboratory rats that aging alters the way brain chemicals help filter out background noise and allow proper processing of complex signals such as speech. The chemicals normally keep that noise from becoming overwhelming.
As a person ages, however, the power of hearing-related nerve signals sent to the brain generally declines. The decrease can be related to a loss of hair cells in the cochlea.
The decrease also can occur when the bones of the middle ear — the structures that conduct sound from the eardrum to the cochlea — stop working as well as they used to. Even excessive earwax can reduce the sound signals transmitted to the brain.
Whatever the cause, Caspary’s research has shown that parts of the brain often respond to the decreased input with chemical changes that reduce the normal filtering and processing effect. The brain may be attempting to increase the volume to compensate for the loss of input.
A younger person’s brain can focus on a softer sound automatically, but an older person trying to compensate for less sound reaching the brain is less nimble at adjusting that biological filter. So a reduction in the filter in an older person makes all sounds louder, including background noise.
“And therefore, speech is not intelligible when it should be intelligible,” Caspary said. “They don’t hear a crisp signal. The signal is sloppy.”
It’s important to learn about how aging changes the way chemicals interact in the brain in regulating the filtering effect. Eventually, he said, the brain’s “inhibitory system” could be treated with drugs to increase the ability to filter sound.
It could be 10 to 20 years before effective drug therapies are developed, but the pace of discovery doesn’t discourage Caspary.
“Science almost always moves in baby steps,” he said. “I personally accepted that a long, long time ago.”
One fertile area for potential drug treatments involves tinnitus, a medical condition that causes people to hear ringing in the ears or noise in the head when no external source is present. Caspary and the other scientists at SIU were the first to demonstrate in an animal model the brain changes that occur at the single-cell level as a result of tinnitus.
Other research from Caspary’s group has been used by pharmaceutical companies in developing patents for potential drugs to treat age-related hearing loss.
“The bottom line is that when we first proposed pharmacotherapy for age-related hearing loss, we were chuckling to ourselves,” Caspary said. “And five years later, we were being contacted by different drug companies.”