The Best of 2004
2005; Lippincott Williams & Wilkins; Volume: 58; Issue: 6 Linguagem: Inglês
10.1097/01.hj.0000324241.60095.8a
ISSN2333-6218
Autores ResumoFigureHearing scientists, in both basic and trans-lational (applied or clinical) research areas, were very busy in 2004, which is not unusual for this group. Readers of audiology journals benefited greatly from many very interesting articles embracing topics from the hair cells to the cortex. Some of the published work has immediate application—something you can take right to the clinic—while other topics are important in laying the groundwork for the future. I hope that many of you have already read these articles. For those who have not yet got through that stack of 2004 journals on your desk, here are some articles you may want to look up. As always, there were far too many hearing science articles last year to mention them all here. But I want to compliment all the authors for their excellent contributions to our audiology literature. GREAT FORTHE CLINICIAN This year, quite a few articles fit into the translational research category. I'll tell you about five that deserve recognition. The first, published in IJA, is on auditory steady-state responses, a topic of great interest to clinicians interested in electrophysiologic threshold testing, particularly in infants and young children. Understanding something as basic as the optimal stimulation rate at various ages in steady-state responses is important in maximizing test efficiency. Joachim Pethe, Roland Mühler, and colleagues help clarify this issue through comparison of amplitude modulation following responses obtained at rates of 40 and 80 Hz. They show that the optimal modulation frequency changes from higher to lower frequency at about 13 years of age. Another auditory evoked potential of current research interest is the mismatch negativity (MMN). Findings to date have been controversial, particularly in relation to the robustness of the response. A paper in JAAA by Catherine Pettigrew, Bruce Murdoch, and their co-investigators shows that the type of stimulus appears tied to the ability to record MMN responses. They report strong MMN responses to tonal stimuli, but responses to speech that were difficult to distinguish. These results are instructive in demonstrating that stimulus type may influence clinical applicability and that this type of careful work is needed if measures such as the MMN are to be of clinical value. While much of the focus of electro-physiologic measures is on applications in children, they have potential value in adult populations as well. David McPherson and Mimi Salamat explore P300 responses and behavioral measures in normal and ADHD young adults and demonstrate, in their research reported in JAAA, that P300 latency and amplitude measures distinguish between these groups to a greater extent than behavioral measures. Such comparisons of behavioral and electrophysiologic measures provide insight into their relative sensitivity to various auditory problems and may also clarify relationships between these different approaches. On another topic, vestibular system function, Gary Jacobson, Devin McCaslin, and colleagues published a paper in JAAA describing a retrospective study of patients with balance problems of apparent central nervous system origin. The study was undertaken to gain understanding of the clinical, electro-physiologic, and anatomic correlates of velocity storage, a brainstem function that extends the lower frequency responses of the vestibular system. They discovered that patients with impaired velocity storage had greater problems in postural stability and gait, and 80% of them showed MRI abnormalities. This work demonstrates the value of carefully obtained clinical data in gaining insight into clinical problems. My final selection in this area concerns the effect of noise on hearing. Van Summers and Michelle Molis, in a study reported in the Journal of Speech, Language, and Hearing Research (JSLHR), examined if reduced audibility alone can account for the decreased speech perception seen in persons with hearing loss. They presented fluctuating and non-fluctuating masker stimuli to listeners with and without hearing loss. It turns out that persons with hearing loss do not derive the same benefit from masker fluctuations as normal hearers do, suggesting that problems are not due to audibility alone. Thus, to truly understand the characteristics and impact of hearing loss, it is important to consider suprathreshold measures of hearing. BEST QUICK READ We turn to our colleagues in Italy for three interesting articles on protection of the ear against noise and ototoxicity. There is still much to learn and several groups are working in these areas. The first article is by Antonio Quaranta and his colleagues, who report in IJA that increasing serum vitamin B12 concentrations protected subjects against temporary threshold shift (TTS). TTS's at 3000 and 4000 Hz—typically the most vulnerable frequencies—were less in subjects who had high concentrations of B12. While much work needs to be done to clarify necessary doses and other issues, this research is helpful in understanding the processes involved in getting and avoiding TTS. While the previous study was completed in humans, animal models provide a method of carefully controlling exposures to drugs and noise as well as putative protective agents. Anna Rita Fetoni and her colleagues in Rome report in IJA that the antioxidant α-tocopherol can successfully interfere with gentam-icin-induced formation of free radicals and may protect our outer hair cells from this form of aminoglycoside ototoxicity. Another piece of the protection story concerns cisplatin. Here, tiopronin, a drug effective in protecting against cisplatin nephrotoxicity, was evaluated by Anna Rita Fetoni and colleagues for its otoprotective potential. They report in another article in IJA that DPOAEs in animals treated with tiopronin were more robust than those in animals treated only with cisplatin, suggesting that hair cells received some protective benefit. NOT READY FOR MEDLINE Regeneration of cochlear hair cells has been a hot topic off and on for a number of years. New discoveries promote a flurry of activity and then the topic slips into the background again as scientists work their way through the many research steps required to gain a clear understanding. A true leader in this research is Ed Rubel at the University of Washington. He provides a candid discussion of the area of hair cell regeneration in Hearing Review with some predictions about the future and what it will take to get there. Understanding normal cell cycles, the role of particular genes in promoting development, and a possible role for stem cells are all important aspects to study. He even touches on how hair cell regeneration relates to hearing aids, a question sure to be on the minds of many audiologists. Not sure what a stem cell is or how it might be of value in hearing? Then check “A Moment in Science” in Audiology Today, where Lisa Cunningham and Lendra Friesen provide a nice summary of characteristics of stem cells and how they might be applied in hearing. In another “Moment” they discuss the role of the Math1 gene in hair cell production. While you have your mind on hair cells, you can find out what's good for them in a Page Ten article in HJ by Kathy Campbell. Here she discusses the general topic of protecting the ear against hearing loss and the role of antioxidants, and provides interesting information about what's happening in our ears at cellular and molecular levels. The previous articles focus on molecular and cellular biology. Neural connections are another part of what makes up the auditory system; this neurobiologic activity is important in guiding our understanding of the brain and behavior. Gail Chermak provides a valuable perspective and some interesting food for thought related to APD in her Pathways contribution in HJ. BEST SPECIAL ISSUE Some years I've selected a Best Special Issue. This year I'm taking a slight diversion due to the publication of a couple of great review articles in 2004. These two articles pack a “one-two punch,” appearing as the first and second articles in the April issue of Ear and Hearing. So could this be considered a mini-special issue? The first article, by Chris Shera, is “Mechanisms of mammalian otoacoustic emission and their implications for the clinical utility of otoacoustic emissions.” Shera is a leader in advancing our understanding of the mechanisms underlying OAEs. In 1999, he and John Guinan proposed a mechanism-based taxonomy that identifies two fundamentally different sources of OAEs. In the current review and discussion of the mechanisms of generation in the context of this taxonomy, he updates us on new information important to the basic understanding of OAEs and their clinical measurement and interpretation. If you have an OAE instrument in your clinic (or even if you don't), this is a must read! On a very different topic but still in the cochlea, Brian Moore discusses “Dead regions in the cochlea: Conceptual foundations, diagnosis, and clinical applications.” The concept of dead regions provides us with a new view, again from a mechanistic standpoint, of what's happening (or not happening) in the cochlea. Moore covers the anatomical, physiological, and psychophysical foundations related to dead regions in a clear, comprehensive, and informative manner. The concept of dead regions is very important in guiding management, as Moore and others have shown that amplification will not help in an area lacking receptors. Actually, put both of these articles on your must-read list! Every audiologist needs to know about the cochlea, and these articles bring us up to date in two interesting and important areas. MOST THOUGHT-PROVOKING Lots of hearing science papers are thought-provoking, so it's difficult to pick just a few, particularly if you are a hearing scientist. I've probably exceeded my quota here, but I do want to bring a number of interesting, thought-provoking topics to your attention. First, I'd like to mention an article that I'm not going to review by Pat Stelma-chowicz, Andrea Pittman, Brenda Hoover, and Dawna Lewis in Ear and Hearing. I'm mentioning it because I really liked it and it certainly fits in my area. But Gus Mueller convinced me it might fit better with hearing aids, so read about it in his section. The first article that I will discuss in this category was published in JSLHR by Penelope Hill, Douglas Hartley, Brian Glasberg, Brian Moore, and David Moore on auditory processing efficiency and temporal resolution in children and adults. This is one of those studies that strives to get at the reasons underlying an observed behavior. Here, Hill et al. focus on the observation that children have higher thresholds in backward-masking tasks than adults. These higher thresholds have been tied to decreased temporal resolution ability, an area of particular interest to those interested in auditory processing disorders and habilitation. While the role of temporal resolution makes sense, it doesn't take subsequent (higher order) processing into account. The authors measured backward masking at various signal-to-masker ratios and found that processing efficiency does have a role in explaining differences in backward-masking thresholds between children and adults. Otoacoustic emissions are widely used clinically, yet the relationship of OAEs to behavioral hearing thresholds is elusive. There are a number of likely reasons for this. One is that DPOAEs measured in the ear canal are thought to represent complex interactions of multiple components. If we could isolate single generators, that might help us relate OAEs to behavioral thresholds. Sounds simple, right? Well, it's not. In research reported in Ear and Hearing, Sumit Dhar and Lauren Shaffer used a suppressor tone as a method of obtaining single-generator DPOAEs and looked at the effects on DP fine structure. They found that the suppressor tone resulted in considerable variability in DP fine structure among individuals and even within the same ear at different frequencies. This article caught my eye because it reminds me that when I interpret OAE data in the clinic, the relationships and answers are not going to be easy or straightforward. I will continue to exercise caution. Sorting out the effects of stimulus characteristics, age, hearing loss, and other factors on sound perception is challenging to researchers who work on these problems. Several studies in 2004 addressed some of these factors and all are worth taking a look at. One factor, stimulus complexity, is of interest because it may help us understand the types of listening situations we find ourselves in every day. John Grose, Joseph Hall, and Emily Buss report in JSLHR that subjects, both with normal hearing and hearing loss, have greater difficulty on tasks where the frequency and/or the amplitude of test stimuli changes randomly and dynamically. It's interesting that such challenging complex stimuli outweigh the effects of hearing loss as a factor of importance. (By the way, this research group has had a busy year. Check out their articles on development of the MLD and temporal fine structure, too.) In another article in JSLHR on the theme of stimulus complexity, Jennifer Lister and Kenton Tarver studied gap detection using spectrally dynamic and random duration in older and younger normal-hearing listeners. Changes in spectral characteristics as well as duration made the stimuli more complex than those used in many previous studies of temporal resolution. Both age groups showed poorer gap detection for dynamic stimuli than invariant stimuli and the task was more difficult for older listeners. This study points again to the importance of controlling stimulus dimensions, and also to the need to use complex stimuli to better understand real-life listening conditions. ALL-AROUND FAVORITES There are always so many good articles in hearing science that it's difficult to pick my All-Around Favorites. But, here goes. These are in no particular order, as they are all favorites. What does a left-ear deficit mean? Perhaps it means that information to your left ear isn't processed as well as that to your right ear. But what does that mean? What are the processes underlying or contributing to a left-ear deficit? These are among the questions that Deborah Moncrieff, James Jerger, and their colleagues sought to answer in a study of event-related auditory potentials in dyslexic children reported in JAAA. They found evidence that factors such as slowed neural conduction and poorer interhemispheric transfer contribute to poorer left-side processing in children with behavioral left-ear deficits. This study also demonstrates the value of physiologic information in understanding mechanisms underlying behavioral characteristics. My second All-Around Favorite from 2004 is a report by Gary Rance, Colette McKay, and David Grayden in Ear and Hearing on perceptual abilities of children with auditory neuropathy. As with adults with auditory neuropathy, poor temporal processing is a key to understanding the perceptual problems these children experience. My reason for picking this article did not rest solely on my affinity to the topic of auditory neuropathy/dyssynchrony. I also liked this work because I know how difficult it must have been to extract useful psychophysical data from children and because of the value such information holds in understanding and, most importantly, managing patients with AN/AD. The third article on my list addresses an interesting problem: How do people hear who have asymmetric hearing loss? And, especially, how do they hear in noise? Do they still benefit from a “binaural advantage”? And, to take it one step further, do children have the same binaural advantages? These are just a few of the questions that Ann Rothpletz, Anne Marie Tharpe, and Wes Grantham tackled in their research reported in JSLHR. This was a thought-provoking topic and article (yes, it could have gone in that category, which is where Brad Stach put it) and it was certainly clinically relevant in managing hearing loss. Their findings on the effects of asymmetric hearing loss relative to binaural advantage and binaural interference, especially in children versus adults, are interesting and surprising. But I'm going to let you read about that for yourselves. CONCLUDING REMARKS I hope you enjoy reading these articles and many others. There are also many basic science journals that contain articles of interest and importance to audiologists. So, don't forget to hop on PubMed the next time you're surfing the net and check out some of these as well. Happy reading!
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