Duane Davis, a volunteer for the Hearing Loss Association of Oregon, is afraid he may turn out to be a living example of the latest research correlating hearing loss with brain atrophy.
Figure. iStockphoto....Image Tools
Although that investigation at the University of Pennsylvania linked hearing loss late in life with cognitive decline,.Davis said he needs no scientific proof that mental processes can feel pulverized by a hearing problem, even when his own brain seems to be working just fine.
“There you are, in a conversation, and you hear something like ‘squeeze me’ instead of ‘excuse me,’ and you are trying to figure it all out,” said Davis, who periodically interrupted his own speech to inquire if he “sounds OK.”
“You have to process the mumbling,” he said. “You are slow to respond. I am actually doing more thinking to overcome my loss of hearing doing all that, but then you get to thinking maybe you should just avoid conversation.”
And when you do that, he said, things can really go downhill. “Stop having conversations, and you stop seeing people.”
And when you stop seeing people, you stop going places, and that's when brain activity is really threatened, he said.
As it turns out, Davis, who noted he has no basis other than common sense to make such a claim, seems to be more or less right, according to the UPenn study funded by the National Institutes of Health. The researchers looked at whether normal variations in hearing ability affect the brain processes required for speech comprehension and whether a strong relationship existed between the loss of brain function and a decline in hearing.
To answer that question, adults 60 to 77 with normal hearing for their age were evaluated by functional magnetic resonance imaging (fMRI). The hearing acuity of each person was assessed by recording the individual's brain responsiveness to increasingly complex sentences, and then by measuring the cortical brain volume within the auditory cortex. (J Neurosci 2011;31:12638-12643). The results showed that those with hearing loss had less brain activity on fMRI scans when listening to complex sentences. And those who had the hearing deficits also had less gray matter in the auditory cortex, suggesting that in certain parts of the brain related to the understanding of speech, atrophy may occur more rapidly when hearing diminishes.
WHICH COMES FIRST?
The findings seem to indicate that the neurologic structures involved in perception and cognition may be negatively affected,, perhaps even seriously so, by hearing loss. This could have implications for anyone at risk for such losses, including those in professions or lifestyles where they are exposed to loud noises, from lumberjacks to iPod listeners.
The study results make a strong case for hearing technology—aids and assistive devices that can help hearing stay normal, said Jonathan Peelle, PhD, lead author of the study and a Research Associate in UPenn's Department of Neurology. But Davis, who already wears hearing aids, wants to know which loss starts first, the one in the ears or the one in the mind? Talk is a stimulant of sorts, he pointed out. Isn't it possible that losing the ability to converse affects the brain?
“I think that there is almost certainly a convergence of many things going on in hearing loss, which includes social interaction such as conversation as well as other physiological and neurological changes,” Peelle said. “The way to really get at this—to examine the chicken versus the egg, if you will—would be to get longitudinal data, following people over the course of five to 10 years, and getting measures of [specific brain] functioning, brain structure, social interaction as well as hearing measures. I'm not aware of any studies like this out there, so I think at this point, we really don't know.”
Figure. Jonathan Pel...Image Tools
Indeed it is a “chicken or the egg question,” said Patricia Kricos, PhD, Professor of Audiology in the Department of Speech, Language and Hearing Sciences at the University of Florida, Gainesville. Research shows pretty clearly that there is a connection between lower levels of cognitive function and hearing loss. The question is: “Can we prove that hearing loss causes it?” she asked. And even if it does, there is no solid proof that the declines can be avoided. Cognitive rehabilitation may show that gains can be made through maintaining attention skills, including listening, she said. But does the loss of that focus occur because of hearing loss, or is it the other way around?
Engagement does appear to have a protective effect, Kricos noted. When hearing diminishes, social interaction often does, too. It becomes easier to “not go bowling” or to “miss that dinner party” due to difficulty in keeping up that interaction with others, which in itself can feel downright isolating. This may be why lonely people are substantially more likely to begin to lose cognitive function. Or, as Davis put it: “In a noisy atmosphere, I don't hear anything but noise, so I avoid parties.”
Figure. Patricia Kri...Image Tools
Peelle also noted that cardiovascular health and fitness are related to activity, which has been shown “over and over to aid brain health.” Assuming that less social interaction also leads to less physical activity, this also could be a predictor of less-optimal brain health, he said. A study on nutritional status and hearing health also suggests that these two go hand-in-glove, which may provide another possible means of hearing protection. (See sidebar.)
A GROWING ISSUE
Age-related changes beyond the cochlea have been a challenge to validate scientifically. Is hearing loss driven by a loss of neurons in the auditory pathway? By degeneration of white matter in the brain stem and hearing centers? By vascular deterioration? By age-related neurochemical changes? All have been proposed, with supporting evidence. But so far, histological proof has been far from definitive.
Frank Lin, MD, PhD, and his colleagues at Johns Hopkins University Center on Aging and Health have found that cognition scores are more likely to be low when age-related hearing loss is greater. Using the National Health and Nutritional Examination Survey data, they found that hearing loss was independently associated with lower results on a standard cognitive test. (J Gerontol A Bio Sci Med Sci 2011; 66A:1131-1136.)
Nationally, people 60 and older already comprise a fifth of the population, and that figure is rising sharply. By the year 2030, that segment will be closer to a third of the population. But it isn't just that the population is getting older, the eldest part of it is aging, too, with the fastest-growing portion being those 85 and older. (Ann N Y Acad Sci 2008;1136:210-217.) Already, hearing loss is prevalent in nearly two-thirds of those 70 and older in the United States, the Hopkins group found. (J Gerontol A Bio Sci Med Sci 2011;66:-582-590.).
So the search has been fairly intense to find or refine a highly accurate, noninvasive test to identify early, subtle changes in hearing. Last year, a team at Northwestern University reviewed studies on factors that contribute to understanding speech in noisy surroundings, which is perhaps the first sign of aging-related hearing loss for many people. When adults struggle to comprehend complex stimuli—chains of words similar to the kind used in the UPenn study—against background noise, their brain stem shows marked changes. These differences are consistent with the perceptions of the participants themselves, who know when listening becomes difficult. This may offer an important clinical tool for assessment and management, the authors concluded. (Trends Amplif 2010;14:73-63.)
And this past year, University of Connecticut researchers studied whether cognitive differences could be detected through hearing tests. Using test batteries in people with brain lesions, which were then compared with the results of others who had no known neurological problems, they found the Dichotic Digits Frequency Patterns test battery to best distinguish those with lesions from the control group. The investigators cautioned, however, that future studies should be undertaken using additional central auditory assessments to determine which can provide the most sensitive and specific test battery. (J Am Acad Audiol 2011;22:342-358.)
Whether highly reliable testing can make a difference rests with how well hearing can be preserved, once a hoped-for early diagnosis is made. Mark Ross, PhD, Professor Emeritus of Audiology at the University of Connecticut, said he is not all that optimistic. Ross published a paper more than 15 years ago showing the many reasons for noncompliance in hearing aid use, from cosmetic concerns to outright denial of anything resembling a disability. In fact, Ross's 1995 article, published in the Journal for the International Federation of Hard of Hearing People, might explain the current dismal adherence to hearing assistive technology, which was determined this year by the Hopkins group to be about 40 percent.
Ross doesn't sound any more confident about hearing aid use in the future, despite new data. “Research pointing to a difference in cognition, maybe it would make a difference,” he said. On the other hand, the psychological barriers are the same as ever—the device may be seen as an admission of old age.
Davis is more upbeat in his view. After all, the coming generations are filled with those who are used to sticking listening mechanisms in their ears, including Bluetooth phones and other attachments. “I bet they won't see much difference from their earbuds,” he said.
DIET AND HEARING PRESERVATION
Can an apple a day help keep hearing loss at bay? A recent study shows a significant link between a good diet and auditory health.
Results from the study suggest that a diet rich in antioxidants—lycopene, vitamins C and E, and magnesium—may have the potential to preserve hearing, at least to some degree. (J Am Acad Audiol 2011;22: 49-58.) The findings seem to demonstrate, apparently for the first time, that the same kind of association between nutrients and hearing that has been documented in animals occurs in people, too.
“At this point, we can't recommend specific levels of nutrients that will provide protection or delay age-related hearing loss,” said Christopher Spankovich, AuD, PhD, lead author of the study. “This may likely be specific to the individual,” added Spankovich, who is an Assistant Research Professor in the Department of Speech, Language and Hearing Sciences at the University of Florida, Gainesville.
The study reviewed data on the eating habits of more than 2,000 adults aged 49 to 99. The conclusion: Dietary health is an important variable to consider in examining the pathogenesis of auditory declines, and some of the same nutrients that help maintain vascular health by antioxidant activity may also influence susceptibility to hearing loss.
“What we can recommend is that you follow the USDA guidelines, reducing saturated fats and increasing vegetables and fruits in the diet,” Spankovich said. “Recommending a healthier diet and lifestyle is not going to hurt anyone. Of course, any changes should be discussed with a primary care physician."
FOCUS ON COGNITION
In our November 2009 special guest-edited issue, M. Kathleen Pichora-Fuller, PhD, and a number of colleagues discussed the intersection between hearing loss, cognitive problems, and tinnitus. Read those articles by accessing this link online: http://bit.ly/HJNovember2009.
© 2011 Lippincott Williams & Wilkins, Inc.