How's That Again?
At the annual meeting of the Association for Research in Otolaryngology in New Orleans in February, Robert D. Frisina, PhD, professor of Otolaryngology at the University of Rochester Medical Center and an adjunct professor at Rochester Institute of Technology, suggested that a great deal of the hearing loss associated with getting older was probably a function of processing, not aural acuity. "Traditionally, scientists studying hearing problems started looking at the ear," said Dr. Frisina. "But we are finding patients with normal ears who still have trouble understanding a conversation. There are many people who have good inner ears who just don't hear well. That's because their brains are aging."
It comes down to information overload, actually. Using sophisticated tests to measure how well the brain processes information, researchers have determined that the brain typically does a smash-up job of isolating, identifying, and comprehending the information collected by the senses: colors and shapes, odors, textures, sounds, and tastes. The brain stem is the sorting mechanism—or should we say device?
Tests indicate that this processing ability, not the hearing itself, is what diminishes as we age—at least in many of the aging who claim not to "hear" well. Using tests that measure a person's ability to hear a sentence buried in background noise, scientists have determined that the ears are collecting the data, but the brain lags behind in sorting it all out. In mice, Frisina's research team has determined, the processing lag usually precedes physical hearing loss, and early problems with the brain's feedback system may make the ears more vulnerable to damage, since the diminution in the brain's filtering ability may expose the hearing mechanism to excessive noise.
It seems the brain's ability to filter out unwanted or unnecessary information begins to decline as people pass through their 40s and into their 50s, according to Frisina. It then becomes difficult keep up with the incoming flood of information, in much the same way a computer with a faulty buffer hesitates and stalls as it tries to keep up with incoming data.
Although high-frequency hearing loss is typical of the aging process, most people can "hear around it" (more correctly stated perhaps, as "think around it"), but Frisina suspects that the feedback asynchrony probably accounts for more of the complaints about not hearing things.
"These problems with the aging brain, which nearly everyone experiences, are on top of problems with our ears, which you may or may not have as you get older," Frisina said. "For many people, even if they can still hear sounds as they get older, they still lose the ability to hear and understand speech, because of these brain problems."
All is not bleak, however. Frisina suggests that, as researchers begin to understand the process better, they may also find some of this problem is caused by chemical imbalances in the aging brain. If so, Dr. Frisina concluded, "It may be that in the future we can balance some of these things out [with drug treatment] and get a general sensory improvement in the aged."