Occasionally, The Audiology Condition posts on scientific studies that catch our interest, not because they necessarily have clinical application, but because they give insight into how hearing works and why hearing is important not only to humans but to other species as well.  

Today’s post looks at tiny organisms less than a millimeter in size.  Who knew they had ears? Who knew they could hear with them? Who knew their hearing could be tested?

Coral larvae are no bigger than fleas but recent research proves that they “hear” sound and use directional hearing in a sophisticated manner to increase their survival odds.  The proof was gathered by observing larvae floating aimless around in water tanks.  Aimless drifting behavior turned intentional, or at least non-random, when speakers in the tanks started playing reef sounds and the larvae headed for the speakers.

For several reasons, this is big news for marine biologists, but also for hearing scientists.  

  • First, it helps explain a crucial coral survival  strategy.  Every month when the full moon comes out, coral larvae use sound navigate to select and settle into the prime real estate of reefs.
  • Second, it establishes the hitherto unknown fact that these tiny creatures have “ear(s)” of some sort.  The form and function of these new ears remains a mystery, but scientists speculate that surface hair cells are disturbed by sound waves traveling through water.  This would be akin to us humans wearing our inner ears–with their 40,000 hair cells– out on our arms or finger tips.

Coral larvae live in a fragile survival system with fragile ears.  It wouldn’t take much noise to confuse the larvae and keep them from landing on a reef.  The scientists hypothesize this may be happening:

 “small boats, shipping, drilling, pile driving and seismic testing” are masking the reef sounds so that the larvae can’t find a safe home, thus providing an explanation for coral’s “well-charted decline in recent decades.”

 

ref:  Coral Larvae Move toward Reef Sounds

photo courtesy of Darwinism in Ruins

Last week’s post on aging and hearing loss concluded that “there is ongoing research to guide present-day decision-making” by consumers and providers. Today’s post contains the promised list of research projects and articles, provided here for easy access and review by all those who believe that hearing health matters.     

 

Clinical Studies

 

As examples, The Lin Research Group is engaged in clinical trials studie, such as the two shown below, with descriptions taken from the Group’s website.  

  • Studying Multiple Outcomes after Aural Rehabilitative Treatment (SMART) Study.  the SMART study completed enrollment in December of 2013.  
    • “an observational longitudinal study of adults who received a hearing aid or cochlear implant. The primary goal of this study was to evaluate the cognitive abilities of study participants before and after treatment in addition to other measures of social and physical functioning. Recently, we also began to measure salivary and hair cortisol levels of study participants as a biomarker of stress. Adults who are 50 years or older who received a hearing aid or cochlear implant for the first time were eligible for this study.”
  • Aging, Cognition, and Hearing Evaluation in Elders Pilot (ACHIEVE-P) Trial. ACHIEVE-P completed enrollment in November of 2015 and has already completed the initial pilot.
    • ACHIEVE-P’s purpose is to “determine if treating hearing loss in older adults can reduce the risk of cognitive decline and dementia.” 
  • Baltimore HEARS Pilot Study. The pilot was completed and “laid the foundation for Access HEARS.”
    • The pilot “test[ed] the feasibility of a community-based intervention to deliver hearing health care to at-risk older adults.  The tailored intervention was delivered in a community setting and involved the provision of hearing screening, an affordable, accessible amplification device and training on communication strategies and expectation management.”

 

Published Research

 

The table below lists some of the numerous, subsequent studies that have or are investigating epidemiology of hearing loss. They analyze impact and efficacy of  hearing aids and cochlear implants on a variety of psychological and socioeconomic factors, including loneliness, anxiety dementia, accessibility, personal mobility, and risk behaviors.

 

Study

Conclusions

Lin FR et al.  Hearing loss and incident dementia. Arch Neurol. 2011;68(2):214-220

 

.  “Hearing loss is independently associated with incident all-cause dementia. Whether hearing loss is a marker for early-stage dementia or is actually a modifiable risk factor for dementia deserves further study.”

Lin FR, Thorpe R, Gordon-Salant S, Ferrucci L. Hearing loss prevalence and risk factors among older adults in the United States. The Journals of Gerontology Series A: Biological Sciences and Medical Sciences. 2011;66(5):582-590. 

“Hearing loss is prevalent in nearly two thirds of adults aged 70 years and older in the U.S. population. Additional research is needed to determine the epidemiological and physiological basis for the protective effect of black race against hearing loss and to determine the role of hearing aids in those with a mild hearing loss.”

 

Goman AM & Lin FR. Prevalence of Hearing Loss by Severity in the United States. Am J Public Health. 2016 Oct;106(10):1820-2. doi: 10.2105/AJPH.2016.303299. Epub 2016 Aug 23.

“Hearing loss directly affects 23% of Americans aged 12 years or older. The majority of these individuals have mild hearing loss; however, moderate loss is more prevalent than mild loss among individuals aged 80 years or older.”

 

Mamo SK et al. Prevalence of Untreated Hearing Loss by Income among Older Adults in the United States. J Health Care Poor Underserved. 2016;27(4):1812-1818.

“Overall, approximately 20 million Americans 60 years or older have an untreated clinically significant hearing loss.”

 

Deal JA et al. Hearing Impairment and Incident Dementia and Cognitive Decline in Older Adults: The Health ABC Study. J Gerontol A Biol Sci Med Sci. 2016 Apr 12. pii: glw069. [Epub ahead of print]

“Hearing Impairment is associated with increased risk of developing dementia in older adults. Randomized trials are needed to determine whether treatment of hearing loss could postpone dementia onset in older adults.”

 

Mamo SK et al.  Hearing Care Intervention for Persons with Dementia: A Pilot Study.   Am J Geriatr Psychiatry. 2017 Jan;25(1):91-101. doi: 10.1016/j.jagp.2016.08.019. Epub 2016 Sep 22

 “Improved communication has the potential to reduce symptom burden and improve quality of life.”

 

Nirmalasari O et al. Age-related hearing loss in older adults with cognitive impairment. Int Psychogeriatr. 2017 Jan;29(1):115-121. doi: 10.1017/S1041610216001459. Epub 2016 Sep 22.

 

“Hearing loss is highly prevalent among older adults with cognitive impairment. Despite high prevalence of hearing loss, hearing aid utilization remains low.”

 

Kim MB et al. Diabetes mellitus and the incidence of hearing loss: a cohort study.   Int J Epidemiol. 2016 Nov 6. pii: dyw243. [Epub ahead of print] 

“In this large cohort study of young and middle-aged men and women, DM was associated with the development of bilateral hearing loss. DM patients have a moderately increased risk of future hearing loss.”

 

Contrera KJ et al. Association of Hearing Impairment and Anxiety in Older Adults. J Aging Health. 2016 Feb 24. pii: 0898264316634571. [Epub ahead of print]

“Hearing impairment is independently associated with greater odds of anxiety symptoms in older adults.”

 

Contrera KJ et al. Change in loneliness after intervention with cochlear implants or hearing aids.  2017: Laryngoscope Jan 6. doi: 10.1002/lary.26424. [Epub ahead of print]

 

Treatment of hearing loss with CIs results in a significant reduction in loneliness symptoms. This improvement was not observed with HAs. We observed differential effects of treatment depending on the baseline loneliness score, with the greatest improvements observed in individuals with the most loneliness symptoms at baseline.

Edwards JD et al. Association of Hearing Impairment and Subsequent Driving Mobility in Older Adults. Gerontologist. 2016 Feb 25. pii: gnw009. [Epub ahead of print

“Although prior research indicates older adults with HI may be at higher risk for crashes, they may not modify driving over time. Further exploration of this issue is required to optimize efforts to improve driving safety and mobility among older adults.”

feature image from daily health headlines