there’s more to the condition than shrinking synaptic power:
In his view, it’s a symptom that can be caused by more than
one problem. His research shows that when a mouse’s ears
lose the myelin that insulates the neurons, the critter expe-
riences the symptoms of hidden hearing loss, even though
its synapses are fine. He theorizes that autoimmune disor-
ders like Guillain-Barré syndrome—which is associated with
food poisoning, the flu, hepatitis, and the Zika virus—strip
the body of this myelin, and so might produce that result.
Colleen Le Prell of the Callier Center for Communication
Disorders in Dallas (the place that gave Kujawa her award) har-
bors a deeper doubt about this new condition. Le Prell, whose
work focuses on preventing human hearing loss, has found
no evidence that recreational noise affects the ear. She asked
adults in their 20s to keep track of the time and volume when
they went to a loud place, and she measured their hearing and
speech-recognition abilities before and after. In participants
who opted for a lot of high-decibel fun, Le Prell found no in-
dication that they experienced any permanent changes. She
considered the sounds produced by wiggling hair cells, the
subjects’ ability to comprehend words in both quiet and bois-
terous environments, and the electrical impulses within the
ear. The kids seemed all right, at least if they quantified their
activities accurately—not a guarantee.
Meanwhile, another group, at University College London,
is trying alongside Mass Eye and Ear to develop a diagnos-
tic test—and to see if those are worth doing in the first place.
According to speech and hearing scientist Tim Schoof, the
group is using the electrode-based exam, as well as tests of
how well participants can decipher specific sounds against
background noise, to compare clamor-averse young people
with adults over 45 who have been exposed to loud environ-
ments. They’ve recruited through musicians’ groups, as well
as shooting- and motor-sports clubs.
Back at Harvard, Kujawa continues to find motivation in
the many emails she gets from distressed people who come
across her research. “They recognize their problems in it,” she
says. “They are looking for answers because the answers we’ve
given them haven’t been very satisfactory.”
Things are starting to look up. Already, a few companies—
some staffed by people who used to work with Kujawa and
Liberman—are working on therapeutics, like chemicals called
neurotrophins that could help neurons regrow their synapses.
If the connections to the brain could blossom again, and the
hair cells were fine, hearing could return to baseline.
Even without treatments, awareness has made life better
for Bassett, in that she now understands what might be hap-
pening inside her head. “It was just such a huge relief to hear
that there’s something wrong,” she says.
“We would be hard-pressed in our society to find
somebody who has never had a noise exposure that was
maybe too loud,” Kujawa says. The Occupational Safety
and Health Administration setsBEFOREaround the nerve fibers licorice red. It’s paint-by- number
science. If only it were so uncomplicated in living humans.
Liberman and Kujawa hope they can combine the anat-
omy lessons from deceased humans and animals with the
aural and brain tests in study participants to decide how to
diagnose hidden hearing loss, understand enough about how
it works to fix it, and lock down its causes precisely enough
that, maybe someday, we can better prevent it.
Before her accident, Bassett had been ultraprotective of her
ears. She began working at airports when she was just 17. Her
first job was answering the phone, but before long she was out
on the runway, chasing away animals, driving fuel trucks, park-
ing planes. “I had a boss who kind of treated me like his own
kid, so he was constantly like, ‘Wear your earplugs; wear your
headphones,’” she says. She even took the plugs to concerts.
Research seems to underscore the importance of protect-
ing your ears from quotidian sounds that you wouldn’t have
given a second thought—even when you’re young and feel
untouchable. Liberman and Maison recently did a study
of college kids: About 35 percent of their subjects, mostly
audiology students, had used safeguards, while the other
65 percent—mostly pop music students at several Boston
schools—had been less careful. “A lot of them are really
abusing their ears,” Liberman says.
Both groups had normal standard audiograms. But when
the scientists looked at the kids’ brains, using a test similar to
Bassett’s, the music students showed more signal from the hair
cells compared with their cochlear neurons. In other words,
some of the message was getting lost. These subjects also
couldn’t recognize words as well when there was background
noise or an echo, or when the sound was sped up.
This was a small pilot study, but Liberman and Maison plan
to gather a larger population of people and track them to see
how their hearing changes over time. Aging, Liberman sus-
pects, isn’t the only thing causing the decline we experience
long-term. Some of it is the result of exposure. “If we lived
on a deserted island and were not constantly barraged by
environmental noises created by human machines that our
bodies did not evolve to protect ourselves against,” he muses,
“would our hearing deteriorate as much as it does?” Old stud-
ies of tribespeople in Sudan in the early 1960s—their ability
pristine compared with city dwellers of the same era—suggest
it would not. Unlike the eyes’ tendency to grow farsighted no
matter what, some of the decline we’ve blamed on age might
be due to how many fire trucks we’ve stood next to.
Other researchers come at hidden hearing loss from
different perspectives. Gabriel Corfas—a neuroscientist
at the University of Michigan’s Kresge Hearing Research
Institute who has collaborated with Liberman—thinks (CONTINUED ON P. 115)
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