New understanding of hearing loss points to earlier intervention, says Sumit Dhar, but getting people to listen is a challenge
Now hear this: odds are, your ears already have started to fail.
One in three adults over 65 suffers from disabling hearing loss, defined as a deficit of 40dB or more. Worldwide, at least 380 million people have a diagnosed hearing insufficiency, although the real number is likely much higher, says Sumit Dhar, chair of Northwestern’s Department of Communication Sciences and Disorders. Age-related hearing loss begins by the third decade of life, far earlier than many people expect, and genetics, noise exposure, disease, and ototoxic medications (like certain antibiotics) can accelerate this decline.
The decline doesn’t always broadcast its arrival, but insidiously erodes the auditory function — first at higher frequencies before gradually descending into the speech frequencies. Even then, the condition may go unrecognized, says Dhar. The loss is slow and therefore easy to discount, presenting a hurdle to intervention. And people often find ways to compensate: lipreading or situational cues, for instance.
But other accommodations, such as avoiding people or places where ear trouble can prove embarrassing, “are not so benign,” Dhar says. These tactics can lead to the social isolation that may play a part in the correlation researchers have found between hearing loss and dementia.
“There’s a strong association, but calling it a causal relationship would be a stretch, given what we know,” says Dhar, who explores the inner ear’s physiology and biophysics. He also tries to understand the barriers to hearing healthcare and develop tools to remove them. He says researchers have theorized that increased cognitive load — a general lack of sensory input due to hearing loss — may also contribute to the apparent relationship between the ears and overall brain health.
What is clear, according to Dhar and colleagues at Northwestern’s Auditory Research Laboratory, is that earlier intervention — rather than waiting to react to an obvious hearing deficit — promises to revolutionize therapy.
“Current treatments include putting a hearing aid on to amplify sound,” says Dhar, a widely published audiology leader who joined Northwestern in 2004. “If the loss is really severe, we put a cochlear implant in. On the horizon, though, are pharmacological, stem cell, and genetic approaches to repairing hearing loss or preventing it in the first place.”
Such approaches require proactive tactics, he says. Until recently, physicians and researchers considered middle age the appropriate time for intervention, but Dhar’s work has shown that age-related hearing loss can be detected as early as 20. By the time a person is 50, “the largest chunk of damage has already occurred.”
“These new treatments need to be started in a preventive way rather than waiting to fix the organ when it’s half dead,” he says. “One challenge is motivating a person to do something once you tell them that they have the beginnings of hearing loss that won’t fully manifest for another 15 or 20 years.”
Dhar’s research is helping shift the therapeutic process earlier. His main focus is on otoacoustic emissions (OAEs), sounds that are generated by the inner ear thanks to the cochlea’s biological amplifier — a selective, nonlinear process that helps boost very soft sounds. OAEs can be detected with tiny, sophisticated microphones inserted into the ear canal. As a diagnostic indicator, these emissions can provide objective, relatively noninvasive information about general auditory health.
“This is one of two tools now used for screening newborn hearing. The infant can be sleeping, and you just place the little mic in the ear and play these tones. The ear generates its reaction to the tones and the mic records it,” Dhar says. The research aims at greater understanding of cochlear function and, ultimately, applications of this knowledge to build sensitive clinical tools to detect ear malfunctions.
The new technology to record OAEs at the highest audible frequencies, where age-related damage is first evident, was developed at Northwestern through a collaboration between Dhar and neurobiologist Jonathan Siegel. Dhar credits Siegel for driving much of the tech development of the ER-10X Probe System, a state-of-the-art hearing-research instrument. The system has been licensed to Etymotic Research, a leading research, development, and manufacturing company in Elk Grove Village, Illinois, that designs products to assess and enhance hearing. The company was cofounded 35 years ago by Mead Killion, a Northwestern doctoral graduate and adjunct faculty member in the School of Communication.
In addition to technological innovations developed at Northwestern, Dhar and his colleagues have created a free online assessment tool (available at cedra.northwestern.edu) to help people make determinations about their ear health with their medical practitioners.
Dhar, a native of Kolkata, India, credits his father, a doctor, and his mother, a social activist, for inspiring him to make a positive difference both within and outside his profession. “My parents helped me see the value in cultivating a philosophy of life that is centered outside of yourself and that seeks to amplify positive efforts for the benefit of others,” says Dhar.