SungHee Kim

Characterization of hearing loss in aged type II diabetics.

Presbycusis - age-related hearing loss - is the number one communicative disorder and a significant chronic medical condition of the aged. Little is known about how type II diabetes, another prevalent age-related medical condition, and presbycusis interact. The present investigation aimed to comprehensively characterize the nature of hearing impairment in aged type II diabetics. Hearing tests measuring both peripheral (cochlea) and central (brainstem and cortex) auditory processing were utilized. The majority of differences between the hearing abilities of the aged diabetics and their age-matched controls were found in measures of inner ear function. For example, large differences were found in pure-tone audiograms, wideband noise and speech reception thresholds, and otoacoustic emissions. The greatest deficits tended to be at low frequencies. In addition, there was a strong tendency for diabetes to affect the right ear more than the left. One possible interpretation is that as one develops presbycusis, the right ear advantage is lost, and this decline is accelerated by diabetes. In contrast, auditory processing tests that measure both peripheral and central processing showed fewer declines between the elderly diabetics and the control group. Consequences of elevated blood sugar levels as possible underlying physiological mechanisms for the hearing loss are discussed.

Effects of age on contralateral suppression of distortion product otoacoustic emissions in human listeners with normal hearing

The auditory efferent system presumably plays a role in enhancing signals in noise and, in particular, speech perception in background noise. This study measured the age-related changes of the medial olivocochlear (MOC) system by comparing distortion product otoacoustic emissions (DPOAEs) with and without contralateral white noise stimulation. Otoacoustic emissions were typically reduced in level (magnitude) when white noise was presented to the contralateral ear. This contralateral suppression (CS) is attributed to activation of the MOC system, which has an inhibitory effect on the outer hair cell (OHC) system. By studying CS on cochlear output in human listeners of different ages, it is possible to describe aging effects on the MOC system. Human subjects were young adult, middle aged and old (n = 10/group). All subjects had normal hearing and middle-ear function based upon standard audiometric criteria. The present study recorded 2f1–f2 DPOAE-grams in response to moderate primary tones (L1 = 75, L2 = 65 dB SPL), from 1 to 6.3 kHz. The principal findings were that DPOAE levels were smaller in the old compared to the young group and that CS declined with age for the middle-aged and old groups. In addition, CS in the 1- to 2-kHz range was greater than in the 4- to 6-kHz range for all ages, but especially for the old group. These findings suggest that a functional decline of the MOC system with age precedes OHC degeneration. Moreover, the MOC system maintains better function in the 1- to 2-kHz range than in the 4- to 6-kHz range as a function of age.

Sex differences in distortion product otoacoustic emissions as a function of age in CBA mice

Age-related hearing loss--presbycusis--is the number one communication problem of the aged. A major contributor to presbycusis is the progressive degeneration of cochlear outer hair cells (OHCs). Distortion product otoacoustic emissions (DPOAEs) are effective in vivo, physiological measures of hearing, assessing the health and functioning of the OHCs in mammals. We and others have previously demonstrated that DPOAE amplitudes decline with age in humans and mice. The present studys objective was to measure age-related declines in the OHCs in CBA mice (slow, progressive age-related hearing loss) by comparing DPOAEs and auditory brainstem responses (ABRs) generated from females and males. Young adult (2.1-2.9 months) and middle-aged CBA (14.0-16.4 months) mice were tested, as well as old CBAs (24.3-29.0 months). DPOAE-grams were obtained with L1 = 65 and L2 = 50 dB SPL, f1/f2 = 1.25, using eight points per octave covering a frequency range from 5.6 to 44.8 kHz (geometric mean frequency). ABRs ranged from 3 to 48 kHz. Analyses revealed that DPOAE levels decreased with age for middle-aged and old male CBAs, but for female CBAs, declines did not occur until old age - after menopause. In contrast, ABR amplitudes for female and male young adult and middle-aged CBAs were the same. Female ABR thresholds were lower than males for old CBAs. In conclusion, we discovered that pre-menopausal CBA female mice have healthier OHCs relative to middle-aged males, but much of this relative advantage is lost post-menopause. Understanding sex differences in age-related sensory disorders will be quite helpful for the goals of preventing, slowing or curing sensory problems in old age for both women and men.

Contralateral suppression of distortion-product otoacoustic emissions declines with age: A comparison of findings in CBA mice with human listeners†

Objectives/Hypothesis: The auditory efferent system plays presumed roles in enhancing signals in noise, maintaining the cochlea for optimal acoustic signal processing, and may have a protective role in preserving auditory function in the face of ototoxic events. The objective of the study was to measure age‐related changes of the medial olivocochlear efferent system in mice by comparing distortion‐product otoacoustic emissions generated with and without contralateral white noise stimulation. Consistent with prior work, distortion‐product otoacoustic emissions were typically reduced in magnitude when white noise was presented to the contralateral ear. This contralateral suppression is attributed to activation of the medial olivocochlear efferent system, which has an inhibitory effect on the cochlear hair cell system. By studying contralateral suppression on cochlear output in subjects of different ages, it is possible to describe aging effects on the medial olivocochlear system. Study Design: CBA mice were divided into three age groups: young adult, middle‐aged, and old‐aged animals (21, 13, and 22 animals per group, respectively), and auditory brainstem responses were obtained before distortion‐product otoacoustic emission testing to assess overall hearing abilities. Methods: 2f1‐f2 distortion‐product otoacoustic emission recordings were obtained from individual subjects (anesthetized with ketamine/xylazine) in each age group under two conditions: 1) in quiet and 2) in the presence of a contralaterally applied wideband noise. Results: Principal findings were that distortion‐product otoacoustic emission levels decreased with age for mice in a way similar to humans, when correcting for the absolute difference in life spans. In addition, contralateral suppression declined in middle‐aged and old‐aged groups relative to the young adults for mice in a manner similar to humans. The contralateral suppression decline at low frequencies preceded that of the decline in distortion‐product otoacoustic emissions with age. Conclusion: Functional decline of the medial olivocochlear efferent system with age precedes outer hair cell degeneration. Loss of medial olivocochlear suppressive function may play a role in the development of presbycusis in both clinical cases and animal models.

Auditory Efferent Feedback System Deficits Precede Age-Related Hearing Loss: Contralateral Suppression of Otoacoustic Emissions in Mice

The C57BL/6J mouse has been a useful model of presbycusis, as it displays an accelerated age‐related peripheral hearing loss. The medial olivocochlear efferent feedback (MOC) system plays a role in suppressing cochlear outer hair cell (OHC) responses, particularly for background noise. Neurons of the MOC system are located in the superior olivary complex, particularly in the dorsomedial periolivary nucleus (DMPO) and in the ventral nucleus of the trapezoid body (VNTB). We previously discovered that the function of the MOC system declines with age prior to OHC degeneration, as measured by contralateral suppression (CS) of distortion product otoacoustic emissions (DPOAEs) in humans and CBA mice. The present study aimed to determine the time course of age changes in MOC function in C57s. DPOAE amplitudes and CS of DPOAEs were collected for C57s from 6 to 40 weeks of age. MOC responses were observed at 6 weeks but were gone at middle (15–30 kHz) and high (30–45 kHz) frequencies by 8 weeks. Quantitative stereological analyses of Nissl sections revealed smaller neurons in the DMPO and VNTB of young adult C57s compared with CBAs. These findings suggest that reduced neuron size may underlie part of the noteworthy rapid decline of the C57 efferent system. In conclusion, the C57 mouse has MOC function at 6 weeks, but it declines quickly, preceding the progression of peripheral age‐related sensitivity deficits and hearing loss in this mouse strain. J. Comp. Neurol. 503:593–604, 2007.

Effect of age on binaural speech intelligibility in normal hearing adults

Abstract Sentence perception performance, in quiet and in background noise, was measured in three groups of adult subjects categorized as young, middle-aged, and elderly. Pure tone audiometric thresholds, measures of inner ear function, obtained in all subjects were within the clinically normal hearing range. The primary purpose of this study was to determine the effect of age on speech perception: a secondary purpose was to determine if the speech recognition problem commonly reported in elderly subjects might be due to alterations at sites central to the peripheral nervous system inner ear. Standardized sentence lists were presented in free field conditions in order to invoke binaural hearing that occurs at the brainstem level, and to simulate everyday speech-in-noise listening conditions. The results indicated: (1) an age effect on speech perception performance in quiet and in noise backgrounds, (2) absolute pure tone thresholds conventionally obtained monaurally do not accurately predict suprathreshold speech perception performance in elderly subjects, and (3) by implication the listening problems of the elderly may be influenced by auditory processing changes upstream of the inner ear.

Acknowledgments to Reviewers

Lee Altenberg Jeffrey Horn Boris Mitavskiy Helio Barbosa Christian Igel Sanaz Mostaghim Alwyn Barry Hisao Ishibuchi T. Murata Ramon Bejar Christian Jacob Olfa Nasraoui Sana Ben Hamida Kim Jingwon Boris Naujoks Peter Bentley Bryant Julstrom Martin Oates Peter Bosman Maarten Keijzer Pedro Oliviera Larry Bull Robert Keller Colin Reeves Mikhail Burtsev James Kennedy Mark Roberts Martin Butz Mathias Kern Frank Rotlauf Carlos Cotta Joshua Knowles Ramon Sagarna Bart Craenen Mario Koppen Kumara Sastry Bruce A. Draper Tim Kovacs Michele Sebag Rolf Drechsler Peter Krause Yann Semet Marc Ebner Gary Lamont Jonathan Shapiro Aniko Ekart Samuel Landau Jim Smith Michael Emmerich Marco Laumanns Bill Spears Fernando Esponda Xavier Llora Chris Stephens Jonathan Fieldsend Sushil L. Louis Susan Stepney Peter Fleming Jose Antonio Lozano Ponnuthurai Suganthan Simon Garrett Bernard Manderick Juergen Symanzik Ruxandra Gorunescu Ester Bernado Mansilla Keiki Takadama Jens Gottlieb Elena Marchiori KC Tan Garry Greenwood James Marshal Jon Timmis Steven Gustafson Martin C. Martin Jano Van Hemert Nikolaus Hansen Helmut Mayer Lyndon While Robert Heckendorn Nick McPhee Martin Zachariasen Francisco Herrera Juan J. Merelo Eckart Zitzler John Holmes