AAAS 2016: Hearing for Life

Topics at this year’s annual meeting of American Association for the Advancement of Sciences (AAAS) ranged from genome editing to the gravitational waves of black holes. Many of the neuroscience-related talks and panels focused on the senses and perception: I heard a lot about hearing this year. Here are some highlights:

Kids: “We tend to think of kids as being the source of noise, not the victims of noise,” said Nan Bernstein Ratner of University of Maryland, College Park, who organized a symposium on effects of noise on children. But not only do small children not have access to the volume control when the TV is too loud, they have not yet mastered the ability to sort out important (speech) sounds from other noise.

Unless their environment is quiet, toddlers have a tough time sorting speech from noise; even the level of noise in a typical day-care can be too high, said Rochelle Newman, also at College Park. “Under 2s have a hard time with just one other voice in background.” For example, see the two videos: Children who hear names they know will turn to the speaker, as Bella does; when the noise is too much, they don’t, like James. A parent could call a child’s name over and over in a crowd or noisy park and the child just may not catch it.

Bella: Infants can successfully recognize their own name only at relatively low levels of background noise. Videos courtesy of “Mind in the Making: Experiments in Children’s Learning,”
James: An infant has more difficulty hearing and responding to names in a noisy environment.

Also, children haven’t yet built up the “auditory dictionary” we have. Suppose someone is giving directions on a busy street, and a truck squeals its brakes; for a split-second the important speech is drowned out. An adult takes “gro,” pause, and “wer” and makes “grocery store” without conscious thought; a child hears just the two parts and makes no sense of it. This idea resonated with me: I have this experience a lot on the DC metro subway system, trying to piece together audio from train speakers that tend to drop out a syllable here and there. This might explain when a child has trouble following directions in an environment where other kids are shouting or outside sounds are blaring; for adults, the trouble would be to notice this is happening and understand that the child may not have heard it all, since we automatically smooth it over.

Premature infants:  For preemies, the goal is to provide an optimal environment to allow the brain to complete its normal maturation, said Amir Lahav of Harvard Medical School. In the womb, fetuses hear only muffled, mainly low-frequency sounds. But an incubator—a necessity for maintaining warmth, food, and shelter—is practically a “noise camp” because it has a high-frequency ventilator fan running constantly. Neonatal care units, with monitors beeping, multiple incubators’ fans running, and people rushing here and there, add more noise. [See also our recent story “Early Birth, Altered Brain Connections”]

To more closely mimic the experience of being in the womb to full term, Lahav and others are “wombifying” incubators; recording mother’s voice and heartbeat and piping that into their child’s incubator, along with trying to stem outside noise. This appears to improve these infants’ ability to hear in noise, which improved their ability to attend to mother’s and all other female voices, said Lahov. [See also our recent story “Nurturing Brain Development in Premature Infants”]

Elders: As we grow older, many of us will experience hearing loss, from losing those top frequencies to growing ever more familiar with the “tip of the tongue” experience. [See also our Cerebrum story “Cognitive Skills and the Aging Brain: What to Expect”]. The extreme form of tip of the tongue is anomia, a type of aphasia that can include trouble speaking. The aphasias, language disorders, and apraxia of speech, a speech disorder, can be misidentified by doctors since trouble understanding and producing speech also are signs of dementia.

“Misdiagnosis can affect quality of care,” said Joseph Duffy at The Mayo Clinic. If apraxia or aphasia is seen as dementia or ALS, treatments could be useless or even harmful, he said. In addition, people would not receive advice on speech-assistive devices and other treatments that could help them. During a press conference on this topic, Robert Voogt, formerly a professor of internal medicine at Eastern Virginia Medical School in Norfolk, introduced himself, spoke about his aphasia, and answered questions using a MiniTalk device, which uses icons and a keyboard as input and can also be programmed to say phrases like, “I have trouble speaking so am talking to you with this computer.”

When Vooght started having trouble speaking, he sought the help of Argye Hillis at Johns Hopkins Hospital, whose research in the area includes imaging for diagnoses and transcranial magnetic stimulation as possible treatment for aphasias. “The three different types of primary progressive aphasia are sometimes indistinguishable early in the course,” Hillis said; she is working to find tests to better distinguish them.

Apraxia of speech can lead to later dementia, perhaps tied to buildup of tau protein in the brain, Duffy said. “When therapies are developed that address tau, early identification will become important,” he said.

The brain can influence how well you hear, and how well you hear also affects the brain, said Frank Lin, also of Johns Hopkins University School of Medicine. “Hearing loss can directly affect our cognitive function, and brain structure,” he said. In many cases, though, functional hearing loss is not an inevitable part of aging. The big question as more our population grows older, he says, is “if we address hearing loss, can we reduce the incidence of cognitive decline over time?”

Research into whether treating hearing loss aggressively can affect rates of dementia is in the pilot-study phase now, Lin said. “Hearing loss may be a late-life modifiable factor [in dementia], so it could be a great target” compared with risk factors that need to be identified earlier in life, like buildup of amyloid beta and tau proteins in the brain.

– Nicky Penttila

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