Research Roundup updates HR readers on some of the latest research and clinical findings related to hearing health care. Where appropriate, sources and original citations are provided, and readers are encouraged to refer to the primary literature for more detailed information. Additionally, related articles can be found and keywords can be searched in the HR Online Archives.

Maternal Thyroid Antibodies Linked to Hearing Loss in Children

Children of pregnant women who have elevated thyroid peroxidase autoantibodies (TPOaAb) during the third trimester have an increased risk of sensorineural hearing loss (SNHL), according to a retrospective study by Dr Ellen Wasserman of the Johns Hopkins Bloomberg School of Public Health, Baltimore, and colleagues published in the March 15 edition of the American Journal of Epidemiology.

The study is said to be the first to evaluate the association between TPOaAb and SNHL, examining stored serum specimens drawn between 1959 and 1965 from pregnant participants in the National Collaborative Perinatal Project in Baltimore. Of the 1,736 children born within the study, 74 cases of SNHL were identified based on audiologic exams given to the children at the age of 8 years. The researchers conclude that, compared with 4.3% of all the children, 22.7% of the children whose mothers had elevated TPOaAb had SNHL.

The findings suggest that the fetal exposure during the third trimester to TPOaAb is somehow linked to impaired hearing or auditory development. The research team is now exploring whether the TPOaAb are related to hormone availability, act in some way on the developing child, or might signal other autoimmune responses that produce neurodevelopmental deficits.

Original Article
Wasserman EE, Nelson K, Rose NR, et al. Maternal thyroid autoantibodies during the third trimester and hearing deficits in children: an epidemiologic assessment. Am J Epidemiol. 2008;167:701-710.

Female Hormone Protects Against Hearing Loss in Women and Men

A new study published in the Journal of Clinical Investigation by Barbara Canlon and colleagues at the Karolinska Institute in Stockholm investigates the role of estradiol-binding proteins (known as estrogen receptors) in response to auditory damage by examining hearing loss recovery in mice with deficiencies in various estrogen receptors. They found that mice deficient in only the estrogen receptor ER-beta had reduced recovery from auditory trauma, and that treatment with ER-beta-binding drugs protected mice from auditory damage.

Hormone-replacement therapy may negatively impact hearing, September 13, 2006 The Insider.

Cochlear Function in Older Infants, September 2003 HR.

Furthermore, not only was ER-beta found in the ears of both male and female mice, but levels of the nerve-protecting protein BDNF were reduced in mice that lacked either ER-beta or aromatase.

The authors therefore concluded that this identification of an auditory-protective role for the estrogen receptor ER-beta may enable the development of new treatments for hearing loss. Source: American Academy for the Advancement of Science.

Original Article
Metlser I, Tahera Y, Simpson E, et al. Estrogen receptor ß protects against acoustic trauma in mice. J Clin Invest. 2008;118:1563-1570. Available at: jci.org/content/vol118/page1563. Accessed April 28, 2008.

OAEs Differ for People with Migraines

New research from Turkey suggests that otoacoustic emissions (OAE) testing shows dysfunction of cochlea and cochlear efferents in patients with migraine. The report by Hayrunnisa Bolay, MD, PhD, and colleagues from the Department of Neurology at Gazi University Hospitals in Ankara appears in the April edition of Cephalalgia.

The research may shed light on the mechanisms behind migraines, including problems related to migraineurs’ discrimination of tones and lateralization of sound—particularly in a noisy environment.

Bolay’s team conducted OAE, puretone audiometry, and speech discrimination testing in both ears of 53 patients with migraine and 41 controls. Among the findings were that, in the migraine group, the mean amplitudes of TEOAEs did not show a significant decrease in response to contralateral sound stimulus, as was the case in the controls. The researchers write that absence of suppression of the TEOAEs by contralateral sound stimulation suggests the presence of dysfunction either in the medial olivocochlear complex in the brainstem or at the synaptic transmission between olivocochlear efferents and outer hair cells. Additionally, the disruption in the contralateral suppression may be one of the mechanisms predisposing migraineurs to phonophobia.

Bolay says that the data provide evidence for subclinical nervous system abnormality that is widely distributed from the cerebral cortex to the neuromuscular junction, and would probably be a characteristic underlying susceptibility to migraine attacks.

Original Article
H Bolay, YA Bayazit, B Gündüz, et al. Subclinical dysfunction of cochlea and cochlear efferents in migraine: an otoacoustic emission study. Cephalalgia. 2008;28 (4):309–317.

Repetitive Transcranial Stimulation for People with Tinnitus Has Potential

Repetitive transcranial magnetic stimulation over the left temporoparietal cortex may be a useful treatment for people who have tinnitus, suggests a preliminary study published in the February issue of the Journal of Neurology, Neurosurgery, and Psychiatry.

Dr Eman Khedr of Assiut University Hospital in Egypt and colleagues compared the effects of different frequencies of repetitive transcranial magnetic stimulation (rTMS) at three frequencies (1 Hz, 10 Hz, and 25 Hz) versus a sham treatment (occipital, 1 Hz) given daily for 2 weeks. These four treatment were randomly provided to 66 patients who had chronic tinnitus. Patients were assessed using the Tinnitus Handicap Inventory, self-ratings of symptoms, and audiometric measures of residual inhibition before, immediately after the 2 weeks’ treatment, and monthly for 4 consecutive months.

Compared with the sham treatment, all three treatment groups experienced a change. A two-factor ANOVA revealed a significant “rTMS” x “time” interaction, with the rTMS producing greater improvement than sham. However, there was no significant difference between the responses to different frequencies of rTMS. The response to rTMS depended on the duration of tinnitus, with patients having tinnitus for the longest periods being the least likely to respond.

The researchers conclude that daily sessions of rTMS over the temporoparietal cortex may be a useful potential treatment avenue for tinnitus.

Original Article
Khedr EM, Rothwell JC, Ahmed MA, El-Atar A. Effect of daily repetitive transcranial magnetic stimulation for treatment of tinnitus: comparison of different stimulus frequencies. J Neurol Neurosurg Psychiatry. 2008;79:212-215.

Working Memory Has Limited “Slots”

A new study by researchers at UC Davis shows how our very short-term “working memory”—memory that allows the brain to stitch together sensory information—operates. The system retains a limited number of high-resolution images for a few seconds, rather than a wider range of fuzzier impressions. The paper is published online in the April 2 edition of Nature, and the work was supported by grants from the National Institute of Mental Health.

Humans rarely move their eyes smoothly. As our eyes flit from object to object, the visual system briefly shuts off to cut down visual “noise,” says Steven J. Luck, professor of psychology at the UC Davis Center for Mind and Brain. The brain gets a series of snapshots of about a quarter-second, separated by brief gaps.

The working memory system smoothes out this jerky sequence of images by retaining memories from each snapshot so that they can be blended together. These memories typically last just a few seconds. “We use working memory hundreds of thousands of times each day without noticing it,” says Luck. The system also seems to be linked to intelligence, he said.

Luck and postdoctoral researcher Weiwei Zhang wanted to test whether working memory stores a fixed, limited number of high-resolution images, or is a more fluid system that can store either a small number of high-resolution images or a large number of low-resolution images.

They showed volunteers a pattern of colored squares for a tenth of a second, and then asked them to recall the color of one of the squares by clicking on a color wheel. Sometimes the subjects would be completely unable to remember the color, and they just clicked at a random location on the color wheel. When subjects could remember the square, however, they usually clicked on a color that was quite close to the original color.

Zhang developed a technique for using these responses to quantify how many items a subject could store in memory and how precise those memories were.

“It’s a trivial task, but it took us years to realize that we should use it,” says Luck. The researchers began the work at the University of Iowa; Luck moved to UC Davis in 2006, and Zhang in 2007.

Tinnitus: Addressing Neurological, Audiological, and Psychological Aspects with Customized Therapy, August 2007 HR.

The evidence shows that working memory acts like a high-resolution camera, retaining three or four features in high detail. Those features allow the brain to link successive images together. However, while most digital cameras allow the user to choose a lower resolution and therefore store more images, the resolution of working memory appears to be constant for a given individual. Individuals do differ in the resolution of each feature and the number of features that can be stored.

People who can store more information in working memory have higher levels of “fluid intelligence,” the ability to solve novel problems, Luck says. Working memory is also important in keeping track of objects that are temporarily blocked from view, and it appears to be used when we need to recognize objects shown in unfamiliar views.

Work by Lisa M. Oakes, another psychology professor at UC Davis, and colleagues has shown that very young infants have fairly primitive working memory abilities. Between the ages of 6 and 10 months, however, they rapidly develop a much more adult-like working memory system.

Outside the visual domain, working memory is used for storing alternatives or intermediate values, for example when adding a string of numbers together, Luck says. It also appears to play an important role in learning new words, perhaps by allowing the sound of a new word to remain active in the listener’s brain until a long-term memory of the word can be formed.

Luck compared the working memory system to the internal memory registers on a computer chip that allow it to make a series of calculations in between referring to the main memory. Our more familiar long-term memory, in contrast, can be used to store large quantities of information for long periods of time, but it is accessed much more slowly, like a computer’s hard drive.

Luck and Zhang are now interested in how working memory operates in people with conditions such as attention deficit/hyperactivity disorder and schizophrenia, and those who have problems in perception and cognition. Source: UC-Davis.

Original Article
Zhang W, Luck SJ. Discrete fixed-resolution representations in visual working memory. Nature. 2008;390:279-281.