Academy Responds to Consumer Reports Hearing Aid Guide 2016

Like Consumer Reports, the American Academy of Audiology places a high priority on providing individuals with hearing loss and their families with easily accessible, accurate information that will address common questions and guide them to appropriate intervention. Because we share a common goal of directing those with hearing loss to meaningful resources that will improve outcomes and satisfaction, we were compelled to draw attention to several inaccuracies in the recent publication that may be misleading.

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Quantifying Six-Minute Walk Induced Gait Deterioration with Inertial Sensors in Multiple Sclerosis Subjects

Publication date: Available online 27 July 2016
Source:Gait & Posture
Author(s): Matthew M. Engelhard, Sriram Raju Dandu, Stephen D. Patek, John C. Lach, Myla D. Goldman
BackgroundThe six-minute walk (6MW) is a common walking outcome in multiple sclerosis (MS) thought to measure fatigability in addition to overall walking disability. However, direct evidence of 6MW induced gait deterioration is limited by the difficulty of measuring qualitative changes in walking.ObjectivesThis study aims to (1) define and validate a measure of fatigue-related gait deterioration based on data from body-worn sensors; and (2) use this measure to detect gait deterioration induced by the 6MW.MethodsGait deterioration was assessed using the Warp Score, a measure of similarity between gait cycles based on dynamic time warping (DTW). Cycles from later minutes were compared to baseline cycles in 89 subjects with MS and 29 controls. Correlation, corrected (partial) correlation, and linear regression were used to quantify relationships to walking and fatigue outcomes.ResultsWarp Scores rose between minute 3 and minute 6 in subjects with mild and moderate disability (p<0.001). Statistically significant correlations (p<0.001) to the MS walking scale (MSWS-12), modified fatigue impact scale (MFIS) physical subscale, and cerebellar and pyramidal functional system scores (FSS) were observed even after controlling for walking speed. Regression of MSWS-12 scores on Warp Scores and walking speed explained 73.9% of response variance. Correlations to individual MSWS-12 and MFIS items strongly suggest a relationship to fatigability.ConclusionThe Warp Score has been validated in MS subjects as an objective measure of fatigue-related gait deterioration. Progressive changes to gait cycles induced by the 6MW often appeared in later minutes, supporting the importance of sustained walking in clinical assessment.



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Reliability and minimum detectable change of the gait profile score for post-stroke patients

Publication date: Available online 26 July 2016
Source:Gait & Posture
Author(s): Gisele Francini Devetak, Suzane Ketlyn Martello, Juliana Carla de Almeida, Katren Pedroso Correa, Dielise Debona Iucksch, Elisangela Ferretti Manffra
The objectives of this work were (i) to determine Gait Profile Score (GPS) for hemiparetic stroke patients, (ii) to evaluate its reliability within and between sessions, and (iii) to establish its minimal detectable change (MDC). Seventeen hemiparetic patients (mean age 54.9±10.5years; 9 men and 8 women; 6 hemiparetic on the left side and 11 on the right side; mean time after stroke 6.1±3.5months) participated in 2 gait assessment sessions within an interval of 2–7 days. Intra-session reliability was obtained from the intraclass correlation coefficient (ICC) between the three strides of each session. Inter-session reliability was estimated by the ICC from the averages of that three strides. GPS value of non paretic lower limb (NPLL) (13.9±2.4°) was greater than that of paretic lower limb (PLL) (12.0±2.8°) and overall GPS (GPS_O) was 13.7±2.5°. The Gait Variable Scores (GVS), GPS and GPS_O exhibited intra-session ICC values between 0.70 and 0.99, suggesting high intra-day stability. Most of GVS exhibited excellent inter-session reliability (ICC between 0.81 and 0.93). Only hip rotation, hip abduction of PLL exhibited moderate reliability with ICC/MDC values of 0.57/10.0° and 0.71/3.1°, respectively. ICC/MDC values of GPS were 0.92/2.3° and 0.93/1.9° for PLL and NPLL, respectively. GPS_O exhibited excellent test-retest reliability (ICC=0.95) and MDC of 1.7°. Given its reliability, the GPS has proven to be a suitable tool for therapeutic assessment of hemiparetic patients after stroke.



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Quantifying Six-Minute Walk Induced Gait Deterioration with Inertial Sensors in Multiple Sclerosis Subjects

Publication date: Available online 27 July 2016
Source:Gait & Posture
Author(s): Matthew M. Engelhard, Sriram Raju Dandu, Stephen D. Patek, John C. Lach, Myla D. Goldman
BackgroundThe six-minute walk (6MW) is a common walking outcome in multiple sclerosis (MS) thought to measure fatigability in addition to overall walking disability. However, direct evidence of 6MW induced gait deterioration is limited by the difficulty of measuring qualitative changes in walking.ObjectivesThis study aims to (1) define and validate a measure of fatigue-related gait deterioration based on data from body-worn sensors; and (2) use this measure to detect gait deterioration induced by the 6MW.MethodsGait deterioration was assessed using the Warp Score, a measure of similarity between gait cycles based on dynamic time warping (DTW). Cycles from later minutes were compared to baseline cycles in 89 subjects with MS and 29 controls. Correlation, corrected (partial) correlation, and linear regression were used to quantify relationships to walking and fatigue outcomes.ResultsWarp Scores rose between minute 3 and minute 6 in subjects with mild and moderate disability (p<0.001). Statistically significant correlations (p<0.001) to the MS walking scale (MSWS-12), modified fatigue impact scale (MFIS) physical subscale, and cerebellar and pyramidal functional system scores (FSS) were observed even after controlling for walking speed. Regression of MSWS-12 scores on Warp Scores and walking speed explained 73.9% of response variance. Correlations to individual MSWS-12 and MFIS items strongly suggest a relationship to fatigability.ConclusionThe Warp Score has been validated in MS subjects as an objective measure of fatigue-related gait deterioration. Progressive changes to gait cycles induced by the 6MW often appeared in later minutes, supporting the importance of sustained walking in clinical assessment.



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Reliability and minimum detectable change of the gait profile score for post-stroke patients

Publication date: Available online 26 July 2016
Source:Gait & Posture
Author(s): Gisele Francini Devetak, Suzane Ketlyn Martello, Juliana Carla de Almeida, Katren Pedroso Correa, Dielise Debona Iucksch, Elisangela Ferretti Manffra
The objectives of this work were (i) to determine Gait Profile Score (GPS) for hemiparetic stroke patients, (ii) to evaluate its reliability within and between sessions, and (iii) to establish its minimal detectable change (MDC). Seventeen hemiparetic patients (mean age 54.9±10.5years; 9 men and 8 women; 6 hemiparetic on the left side and 11 on the right side; mean time after stroke 6.1±3.5months) participated in 2 gait assessment sessions within an interval of 2–7 days. Intra-session reliability was obtained from the intraclass correlation coefficient (ICC) between the three strides of each session. Inter-session reliability was estimated by the ICC from the averages of that three strides. GPS value of non paretic lower limb (NPLL) (13.9±2.4°) was greater than that of paretic lower limb (PLL) (12.0±2.8°) and overall GPS (GPS_O) was 13.7±2.5°. The Gait Variable Scores (GVS), GPS and GPS_O exhibited intra-session ICC values between 0.70 and 0.99, suggesting high intra-day stability. Most of GVS exhibited excellent inter-session reliability (ICC between 0.81 and 0.93). Only hip rotation, hip abduction of PLL exhibited moderate reliability with ICC/MDC values of 0.57/10.0° and 0.71/3.1°, respectively. ICC/MDC values of GPS were 0.92/2.3° and 0.93/1.9° for PLL and NPLL, respectively. GPS_O exhibited excellent test-retest reliability (ICC=0.95) and MDC of 1.7°. Given its reliability, the GPS has proven to be a suitable tool for therapeutic assessment of hemiparetic patients after stroke.



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Quantifying Six-Minute Walk Induced Gait Deterioration with Inertial Sensors in Multiple Sclerosis Subjects

Publication date: Available online 27 July 2016
Source:Gait & Posture
Author(s): Matthew M. Engelhard, Sriram Raju Dandu, Stephen D. Patek, John C. Lach, Myla D. Goldman
BackgroundThe six-minute walk (6MW) is a common walking outcome in multiple sclerosis (MS) thought to measure fatigability in addition to overall walking disability. However, direct evidence of 6MW induced gait deterioration is limited by the difficulty of measuring qualitative changes in walking.ObjectivesThis study aims to (1) define and validate a measure of fatigue-related gait deterioration based on data from body-worn sensors; and (2) use this measure to detect gait deterioration induced by the 6MW.MethodsGait deterioration was assessed using the Warp Score, a measure of similarity between gait cycles based on dynamic time warping (DTW). Cycles from later minutes were compared to baseline cycles in 89 subjects with MS and 29 controls. Correlation, corrected (partial) correlation, and linear regression were used to quantify relationships to walking and fatigue outcomes.ResultsWarp Scores rose between minute 3 and minute 6 in subjects with mild and moderate disability (p<0.001). Statistically significant correlations (p<0.001) to the MS walking scale (MSWS-12), modified fatigue impact scale (MFIS) physical subscale, and cerebellar and pyramidal functional system scores (FSS) were observed even after controlling for walking speed. Regression of MSWS-12 scores on Warp Scores and walking speed explained 73.9% of response variance. Correlations to individual MSWS-12 and MFIS items strongly suggest a relationship to fatigability.ConclusionThe Warp Score has been validated in MS subjects as an objective measure of fatigue-related gait deterioration. Progressive changes to gait cycles induced by the 6MW often appeared in later minutes, supporting the importance of sustained walking in clinical assessment.



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Reliability and minimum detectable change of the gait profile score for post-stroke patients

Publication date: Available online 26 July 2016
Source:Gait & Posture
Author(s): Gisele Francini Devetak, Suzane Ketlyn Martello, Juliana Carla de Almeida, Katren Pedroso Correa, Dielise Debona Iucksch, Elisangela Ferretti Manffra
The objectives of this work were (i) to determine Gait Profile Score (GPS) for hemiparetic stroke patients, (ii) to evaluate its reliability within and between sessions, and (iii) to establish its minimal detectable change (MDC). Seventeen hemiparetic patients (mean age 54.9±10.5years; 9 men and 8 women; 6 hemiparetic on the left side and 11 on the right side; mean time after stroke 6.1±3.5months) participated in 2 gait assessment sessions within an interval of 2–7 days. Intra-session reliability was obtained from the intraclass correlation coefficient (ICC) between the three strides of each session. Inter-session reliability was estimated by the ICC from the averages of that three strides. GPS value of non paretic lower limb (NPLL) (13.9±2.4°) was greater than that of paretic lower limb (PLL) (12.0±2.8°) and overall GPS (GPS_O) was 13.7±2.5°. The Gait Variable Scores (GVS), GPS and GPS_O exhibited intra-session ICC values between 0.70 and 0.99, suggesting high intra-day stability. Most of GVS exhibited excellent inter-session reliability (ICC between 0.81 and 0.93). Only hip rotation, hip abduction of PLL exhibited moderate reliability with ICC/MDC values of 0.57/10.0° and 0.71/3.1°, respectively. ICC/MDC values of GPS were 0.92/2.3° and 0.93/1.9° for PLL and NPLL, respectively. GPS_O exhibited excellent test-retest reliability (ICC=0.95) and MDC of 1.7°. Given its reliability, the GPS has proven to be a suitable tool for therapeutic assessment of hemiparetic patients after stroke.



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Hearing test may identify autism risk

Researchers have identified an inner ear deficiency in children with Autism that may impact their ability to recognize speech.

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Hearing test may identify autism risk

Researchers have identified an inner ear deficiency in children with Autism that may impact their ability to recognize speech.

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Hearing test may identify autism risk

Researchers have identified an inner ear deficiency in children with Autism that may impact their ability to recognize speech.

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Seasonal variations in auditory processing in the inferior colliculus of Eptesicus fuscus

Publication date: Available online 26 July 2016
Source:Hearing Research
Author(s): Kimberly E. Miller, Kaitlyn Barr, Mitchell Krawczyk, Ellen Covey
Eptesicus fuscus is typical of temperate zone bats in that both sexes undergo marked seasonal changes in behavior, endocrine status, and reproductive status. Acoustic communication plays a key role in many seasonal behaviors. For example, males emit specialized vocalizations during mating in the fall, and females use different specialized vocalizations to communicate with infants in late spring. Bats of both sexes use echolocation for foraging during times of activity, but engage in little sound-directed behavior during torpor and hibernation in winter. Auditory processing might be expected to reflect these marked seasonal changes.To explore the possibility that seasonal changes in hormonal status could drive functional plasticity in the central auditory system, we examined responses of single neurons in the inferior colliculus throughout the year.The average first-spike latency in females varied seasonally, almost doubling in spring compared to other times of year. First-spike latencies in males remained relatively stable throughout the year. Latency jitter for both sexes was higher in winter and spring than in summer or fall.Females had more burst responders than other discharge patterns throughout the year whereas males had more transient responders at all times of year except fall, when burst responses were the predominant type. The percentage of simple discharge patterns (sustained and transient) was higher in males than females in the spring and higher in females than males in the fall.In females, the percentage of shortpass duration-tuned neurons doubled in summer and remained elevated through fall and early winter. In males, the percentage of shortpass duration-tuned cells increased in spring and the percentage of bandpass duration-tuned cells doubled in the fall.These findings suggest that there are clear seasonal changes in basic response characteristics of midbrain auditory neurons in Eptesicus, especially in temporal response properties and duration sensitivity. Moreover, the pattern of changes is different in males and females, suggesting that hormone-driven plasticity adjusts central auditory processing to fit the characteristics of vocalizations specific to seasonal behavioral patterns.



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Acoustic input impedance of the avian inner ear measured in ostrich (Struthio camelus)

Publication date: Available online 26 July 2016
Source:Hearing Research
Author(s): Pieter G.G. Muyshondt, Peter Aerts, Joris J.J. Dirckx
In both mammals and birds, the mechanical behavior of the middle ear structures is affected by the mechanical impedance of the inner ear. In this study, the aim was to quantify the acoustic impedance of the avian inner ear in the ostrich, which allows us to determine the effect on columellar vibrations and middle ear power flow in future studies. To determine the inner ear impedance, vibrations of the columella were measured for both the quasi-static and acoustic stimulus frequencies. In the frequency range of 0.3-4 kHz, we used electromagnetic stimulation of the ossicle and a laser Doppler vibrometer to measure the vibration response. At low frequencies, harmonic displacements were imposed on the columella using piezo stimulation and the resulting force response was measured with a force sensor. From these measurement data, the acoustic impedance of the inner ear could be determined. A simple RLC model in series of the impedance measurements resulted in a stiffness reactance of KIE = 0.20·10¹² Pa/m³, an inertial impedance of MIE = 0.652·10⁶ Pa·s²/m³, and a resistance of RIE = 1.57·10⁹ Pa·s/m. We found that values of the inner ear impedance in the ostrich are one to two orders in magnitude smaller than what is found in mammal ears.



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Cortical reorganization in postlingually deaf cochlear implant users: intra-modal and cross-modal considerations

Publication date: Available online 26 July 2016
Source:Hearing Research
Author(s): Maren Stropahl, Ling-Chia Chen, Stefan Debener
With the advances of cochlear implant (CI) technology, many deaf individuals can partially regain their hearing ability. However, there is a large variation in the level of recovery. Cortical changes induced by hearing deprivation and restoration with CIs have been thought to contribute to this variation. The current review aims to identify these cortical changes in postlingually deaf CI users and discusses their maladaptive or adaptive relationship to the CI outcome. Overall, intra-modal and cross-modal reorganization patterns have been identified in postlingually deaf CI users in visual and in auditory cortex. Even though cross-modal activation in auditory cortex is considered as maladaptive for speech recovery in CI users, a similar activation relates positively to lip reading skills. Furthermore, cross-modal activation of the visual cortex seems to be adaptive for speech recognition. Currently available evidence points to an involvement of further brain areas and suggests that a focus on the reversal of visual take-over of the auditory cortex may be too limited. Future investigations should consider expanded cortical as well as multi-sensory processing and capture different hierarchical processing steps. Furthermore, prospective longitudinal designs are needed to track the dynamics of cortical plasticity that takes place before and after implantation.



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Atypical white-matter microstructure in congenitally deaf adults: a region of interest and tractography study using diffusion-tensor imaging

Publication date: Available online 26 July 2016
Source:Hearing Research
Author(s): Christina M. Karns, Courtney Stevens, Mark W. Dow, Emily Schorr, Helen J. Neville
Considerable research documents the cross-modal reorganization of auditory cortices as a consequence of congenital deafness, with remapped functions that include visual and somatosensory processing of both linguistic and nonlinguistic information. Structural changes accompany this cross-modal neuroplasticity, but precisely which specific structural changes accompany congenital and early deafness and whether there are group differences in hemispheric asymmetries remain to be established. Here, we used diffusion tensor imaging (DTI) to examine microstructural white matter changes accompanying cross-modal reorganization in 23 deaf adults who were genetically, profoundly, and congenitally deaf, having learned sign language from infancy with 26 hearing controls who participated in our previous fMRI studies of cross-modal neuroplasticity. In contrast to prior literature using a whole-brain approach, we introduce a semiautomatic method for demarcating auditory regions in which regions of interest (ROIs) are defined on the normalized white matter skeleton for all participants, projected into each participants native space, and manually constrained to anatomical boundaries. White-matter ROIs were left and right Heschl’s gyrus (HG), left and right anterior superior temporal gyrus (aSTG), left and right posterior superior temporal gyrus (pSTG), as well as one tractography-defined region in the splenium of the corpus callosum connecting homologous left and right superior temporal regions (pCC). Within these regions, we measured fractional anisotropy (FA), radial diffusivity (RD), axial diffusivity (AD), and white-matter volume. Congenitally deaf adults had reduced FA and volume in white matter structures underlying bilateral HG, aSTG, pSTG, and reduced FA in pCC. In HG and pCC, this reduction in FA corresponded with increased RD, but differences in aSTG and pSTG could not be localized to alterations in RD or AD. Direct statistical tests of hemispheric asymmetries in these differences indicated the most prominent effects in pSTG, where the largest differences between groups occurred in the right hemisphere. Other regions did not show significant hemispheric asymmetries in group differences. Taken together, these results indicate that atypical white matter microstructure and reduced volume underlies regions of superior temporal primary and association auditory cortex and introduce a robust method for quantifying volumetric and white matter microstructural differences that can be applied to future studies of special populations.



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Plasticity in bilateral superior temporal cortex: effects of deafness and cochlear implantation on auditory and visual speech processing

Publication date: Available online 26 July 2016
Source:Hearing Research
Author(s): Carly A. Anderson, Diane S. Lazard, Douglas EH. Hartley
While many individuals can benefit substantially from cochlear implantation, the ability to perceive and understand auditory speech with a cochlear implant (CI) remains highly variable amongst adult recipients. Importantly, auditory performance with a CI cannot be reliably predicted based solely on routinely obtained information regarding clinical characteristics of the CI candidate. This review argues that central factors, notably cortical function and plasticity, should also be considered as important contributors to the observed individual variability in CI outcome. Superior temporal cortex (STC), including auditory association areas, plays a crucial role in the processing of auditory and visual speech information. The current review considers evidence of cortical plasticity within bilateral STC, and how these effects may explain variability in CI outcome. Furthermore, evidence of audio-visual interactions in temporal and occipital cortices is examined, and relation to CI outcome is discussed. To date, longitudinal examination of changes in cortical function and plasticity over the period of rehabilitation with a CI has been restricted by methodological challenges. The application of functional near-infrared spectroscopy (fNIRS) in studying cortical function in CI users is becoming increasingly recognised as a potential solution to these problems. Here we suggest that fNIRS offers a powerful neuroimaging tool to elucidate the relationship between audio-visual interactions, cortical plasticity during deafness and following cochlear implantation, and individual variability in auditory performance with a CI.



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The effect of progressive hearing loss on the morphology of endbulbs of Held and bushy cells

Publication date: Available online 26 July 2016
Source:Hearing Research
Author(s): Catherine J. Connelly, David K. Ryugo, Michael A. Muniak
Studies of congenital and early-onset deafness have demonstrated that an absence of peripheral sound-evoked activity in the auditory nerve causes pathological changes in central auditory structures. The aim of this study was to establish whether progressive acquired hearing loss could lead to similar brain changes that would degrade the precision of signal transmission. We used complementary physiologic hearing tests and microscopic techniques to study the combined effect of both magnitude and duration of hearing loss on one of the first auditory synapses in the brain, the endbulb of Held (EB), along with its bushy cell (BC) target in the anteroventral cochlear nucleus. We compared two hearing mouse strains (CBA/Ca and heterozygous shaker-2^+/-) against a model of early-onset progressive hearing loss (DBA/2) and a model of congenital deafness (homozygous shaker-2^-/-), examining each strain at 1, 3, and 6 months of age. Furthermore, we employed a frequency model of the mouse cochlear nucleus to constrain our analyses to regions most likely to exhibit graded changes in hearing function with time. No significant differences in the gross morphology of EB or BC structure were observed in 1-month-old animals, indicating uninterrupted development. However, in animals with hearing loss, both EBs and BCs exhibited a graded reduction in size that paralleled the hearing loss, with the most severe pathology seen in deaf 6-month-old shaker-2^-/- mice. Ultrastructural pathologies associated with hearing loss were less dramatic: minor changes were observed in terminal size but mitochondrial fraction and postsynaptic densities remained relatively stable. These results indicate that acquired progressive hearing loss can have consequences on auditory brain structure, with prolonged loss leading to greater pathologies. Our findings suggest a role for early intervention with assistive devices in order to mitigate long-term pathology and loss of function.



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Seasonal variations in auditory processing in the inferior colliculus of Eptesicus fuscus

Publication date: Available online 26 July 2016
Source:Hearing Research
Author(s): Kimberly E. Miller, Kaitlyn Barr, Mitchell Krawczyk, Ellen Covey
Eptesicus fuscus is typical of temperate zone bats in that both sexes undergo marked seasonal changes in behavior, endocrine status, and reproductive status. Acoustic communication plays a key role in many seasonal behaviors. For example, males emit specialized vocalizations during mating in the fall, and females use different specialized vocalizations to communicate with infants in late spring. Bats of both sexes use echolocation for foraging during times of activity, but engage in little sound-directed behavior during torpor and hibernation in winter. Auditory processing might be expected to reflect these marked seasonal changes.To explore the possibility that seasonal changes in hormonal status could drive functional plasticity in the central auditory system, we examined responses of single neurons in the inferior colliculus throughout the year.The average first-spike latency in females varied seasonally, almost doubling in spring compared to other times of year. First-spike latencies in males remained relatively stable throughout the year. Latency jitter for both sexes was higher in winter and spring than in summer or fall.Females had more burst responders than other discharge patterns throughout the year whereas males had more transient responders at all times of year except fall, when burst responses were the predominant type. The percentage of simple discharge patterns (sustained and transient) was higher in males than females in the spring and higher in females than males in the fall.In females, the percentage of shortpass duration-tuned neurons doubled in summer and remained elevated through fall and early winter. In males, the percentage of shortpass duration-tuned cells increased in spring and the percentage of bandpass duration-tuned cells doubled in the fall.These findings suggest that there are clear seasonal changes in basic response characteristics of midbrain auditory neurons in Eptesicus, especially in temporal response properties and duration sensitivity. Moreover, the pattern of changes is different in males and females, suggesting that hormone-driven plasticity adjusts central auditory processing to fit the characteristics of vocalizations specific to seasonal behavioral patterns.



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Acoustic input impedance of the avian inner ear measured in ostrich (Struthio camelus)

Publication date: Available online 26 July 2016
Source:Hearing Research
Author(s): Pieter G.G. Muyshondt, Peter Aerts, Joris J.J. Dirckx
In both mammals and birds, the mechanical behavior of the middle ear structures is affected by the mechanical impedance of the inner ear. In this study, the aim was to quantify the acoustic impedance of the avian inner ear in the ostrich, which allows us to determine the effect on columellar vibrations and middle ear power flow in future studies. To determine the inner ear impedance, vibrations of the columella were measured for both the quasi-static and acoustic stimulus frequencies. In the frequency range of 0.3-4 kHz, we used electromagnetic stimulation of the ossicle and a laser Doppler vibrometer to measure the vibration response. At low frequencies, harmonic displacements were imposed on the columella using piezo stimulation and the resulting force response was measured with a force sensor. From these measurement data, the acoustic impedance of the inner ear could be determined. A simple RLC model in series of the impedance measurements resulted in a stiffness reactance of KIE = 0.20·10¹² Pa/m³, an inertial impedance of MIE = 0.652·10⁶ Pa·s²/m³, and a resistance of RIE = 1.57·10⁹ Pa·s/m. We found that values of the inner ear impedance in the ostrich are one to two orders in magnitude smaller than what is found in mammal ears.



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Cortical reorganization in postlingually deaf cochlear implant users: intra-modal and cross-modal considerations

Publication date: Available online 26 July 2016
Source:Hearing Research
Author(s): Maren Stropahl, Ling-Chia Chen, Stefan Debener
With the advances of cochlear implant (CI) technology, many deaf individuals can partially regain their hearing ability. However, there is a large variation in the level of recovery. Cortical changes induced by hearing deprivation and restoration with CIs have been thought to contribute to this variation. The current review aims to identify these cortical changes in postlingually deaf CI users and discusses their maladaptive or adaptive relationship to the CI outcome. Overall, intra-modal and cross-modal reorganization patterns have been identified in postlingually deaf CI users in visual and in auditory cortex. Even though cross-modal activation in auditory cortex is considered as maladaptive for speech recovery in CI users, a similar activation relates positively to lip reading skills. Furthermore, cross-modal activation of the visual cortex seems to be adaptive for speech recognition. Currently available evidence points to an involvement of further brain areas and suggests that a focus on the reversal of visual take-over of the auditory cortex may be too limited. Future investigations should consider expanded cortical as well as multi-sensory processing and capture different hierarchical processing steps. Furthermore, prospective longitudinal designs are needed to track the dynamics of cortical plasticity that takes place before and after implantation.



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Atypical white-matter microstructure in congenitally deaf adults: a region of interest and tractography study using diffusion-tensor imaging

Publication date: Available online 26 July 2016
Source:Hearing Research
Author(s): Christina M. Karns, Courtney Stevens, Mark W. Dow, Emily Schorr, Helen J. Neville
Considerable research documents the cross-modal reorganization of auditory cortices as a consequence of congenital deafness, with remapped functions that include visual and somatosensory processing of both linguistic and nonlinguistic information. Structural changes accompany this cross-modal neuroplasticity, but precisely which specific structural changes accompany congenital and early deafness and whether there are group differences in hemispheric asymmetries remain to be established. Here, we used diffusion tensor imaging (DTI) to examine microstructural white matter changes accompanying cross-modal reorganization in 23 deaf adults who were genetically, profoundly, and congenitally deaf, having learned sign language from infancy with 26 hearing controls who participated in our previous fMRI studies of cross-modal neuroplasticity. In contrast to prior literature using a whole-brain approach, we introduce a semiautomatic method for demarcating auditory regions in which regions of interest (ROIs) are defined on the normalized white matter skeleton for all participants, projected into each participants native space, and manually constrained to anatomical boundaries. White-matter ROIs were left and right Heschl’s gyrus (HG), left and right anterior superior temporal gyrus (aSTG), left and right posterior superior temporal gyrus (pSTG), as well as one tractography-defined region in the splenium of the corpus callosum connecting homologous left and right superior temporal regions (pCC). Within these regions, we measured fractional anisotropy (FA), radial diffusivity (RD), axial diffusivity (AD), and white-matter volume. Congenitally deaf adults had reduced FA and volume in white matter structures underlying bilateral HG, aSTG, pSTG, and reduced FA in pCC. In HG and pCC, this reduction in FA corresponded with increased RD, but differences in aSTG and pSTG could not be localized to alterations in RD or AD. Direct statistical tests of hemispheric asymmetries in these differences indicated the most prominent effects in pSTG, where the largest differences between groups occurred in the right hemisphere. Other regions did not show significant hemispheric asymmetries in group differences. Taken together, these results indicate that atypical white matter microstructure and reduced volume underlies regions of superior temporal primary and association auditory cortex and introduce a robust method for quantifying volumetric and white matter microstructural differences that can be applied to future studies of special populations.



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Plasticity in bilateral superior temporal cortex: effects of deafness and cochlear implantation on auditory and visual speech processing

Publication date: Available online 26 July 2016
Source:Hearing Research
Author(s): Carly A. Anderson, Diane S. Lazard, Douglas EH. Hartley
While many individuals can benefit substantially from cochlear implantation, the ability to perceive and understand auditory speech with a cochlear implant (CI) remains highly variable amongst adult recipients. Importantly, auditory performance with a CI cannot be reliably predicted based solely on routinely obtained information regarding clinical characteristics of the CI candidate. This review argues that central factors, notably cortical function and plasticity, should also be considered as important contributors to the observed individual variability in CI outcome. Superior temporal cortex (STC), including auditory association areas, plays a crucial role in the processing of auditory and visual speech information. The current review considers evidence of cortical plasticity within bilateral STC, and how these effects may explain variability in CI outcome. Furthermore, evidence of audio-visual interactions in temporal and occipital cortices is examined, and relation to CI outcome is discussed. To date, longitudinal examination of changes in cortical function and plasticity over the period of rehabilitation with a CI has been restricted by methodological challenges. The application of functional near-infrared spectroscopy (fNIRS) in studying cortical function in CI users is becoming increasingly recognised as a potential solution to these problems. Here we suggest that fNIRS offers a powerful neuroimaging tool to elucidate the relationship between audio-visual interactions, cortical plasticity during deafness and following cochlear implantation, and individual variability in auditory performance with a CI.



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The effect of progressive hearing loss on the morphology of endbulbs of Held and bushy cells

Publication date: Available online 26 July 2016
Source:Hearing Research
Author(s): Catherine J. Connelly, David K. Ryugo, Michael A. Muniak
Studies of congenital and early-onset deafness have demonstrated that an absence of peripheral sound-evoked activity in the auditory nerve causes pathological changes in central auditory structures. The aim of this study was to establish whether progressive acquired hearing loss could lead to similar brain changes that would degrade the precision of signal transmission. We used complementary physiologic hearing tests and microscopic techniques to study the combined effect of both magnitude and duration of hearing loss on one of the first auditory synapses in the brain, the endbulb of Held (EB), along with its bushy cell (BC) target in the anteroventral cochlear nucleus. We compared two hearing mouse strains (CBA/Ca and heterozygous shaker-2^+/-) against a model of early-onset progressive hearing loss (DBA/2) and a model of congenital deafness (homozygous shaker-2^-/-), examining each strain at 1, 3, and 6 months of age. Furthermore, we employed a frequency model of the mouse cochlear nucleus to constrain our analyses to regions most likely to exhibit graded changes in hearing function with time. No significant differences in the gross morphology of EB or BC structure were observed in 1-month-old animals, indicating uninterrupted development. However, in animals with hearing loss, both EBs and BCs exhibited a graded reduction in size that paralleled the hearing loss, with the most severe pathology seen in deaf 6-month-old shaker-2^-/- mice. Ultrastructural pathologies associated with hearing loss were less dramatic: minor changes were observed in terminal size but mitochondrial fraction and postsynaptic densities remained relatively stable. These results indicate that acquired progressive hearing loss can have consequences on auditory brain structure, with prolonged loss leading to greater pathologies. Our findings suggest a role for early intervention with assistive devices in order to mitigate long-term pathology and loss of function.



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Seasonal variations in auditory processing in the inferior colliculus of Eptesicus fuscus

Publication date: Available online 26 July 2016
Source:Hearing Research
Author(s): Kimberly E. Miller, Kaitlyn Barr, Mitchell Krawczyk, Ellen Covey
Eptesicus fuscus is typical of temperate zone bats in that both sexes undergo marked seasonal changes in behavior, endocrine status, and reproductive status. Acoustic communication plays a key role in many seasonal behaviors. For example, males emit specialized vocalizations during mating in the fall, and females use different specialized vocalizations to communicate with infants in late spring. Bats of both sexes use echolocation for foraging during times of activity, but engage in little sound-directed behavior during torpor and hibernation in winter. Auditory processing might be expected to reflect these marked seasonal changes.To explore the possibility that seasonal changes in hormonal status could drive functional plasticity in the central auditory system, we examined responses of single neurons in the inferior colliculus throughout the year.The average first-spike latency in females varied seasonally, almost doubling in spring compared to other times of year. First-spike latencies in males remained relatively stable throughout the year. Latency jitter for both sexes was higher in winter and spring than in summer or fall.Females had more burst responders than other discharge patterns throughout the year whereas males had more transient responders at all times of year except fall, when burst responses were the predominant type. The percentage of simple discharge patterns (sustained and transient) was higher in males than females in the spring and higher in females than males in the fall.In females, the percentage of shortpass duration-tuned neurons doubled in summer and remained elevated through fall and early winter. In males, the percentage of shortpass duration-tuned cells increased in spring and the percentage of bandpass duration-tuned cells doubled in the fall.These findings suggest that there are clear seasonal changes in basic response characteristics of midbrain auditory neurons in Eptesicus, especially in temporal response properties and duration sensitivity. Moreover, the pattern of changes is different in males and females, suggesting that hormone-driven plasticity adjusts central auditory processing to fit the characteristics of vocalizations specific to seasonal behavioral patterns.



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Acoustic input impedance of the avian inner ear measured in ostrich (Struthio camelus)

Publication date: Available online 26 July 2016
Source:Hearing Research
Author(s): Pieter G.G. Muyshondt, Peter Aerts, Joris J.J. Dirckx
In both mammals and birds, the mechanical behavior of the middle ear structures is affected by the mechanical impedance of the inner ear. In this study, the aim was to quantify the acoustic impedance of the avian inner ear in the ostrich, which allows us to determine the effect on columellar vibrations and middle ear power flow in future studies. To determine the inner ear impedance, vibrations of the columella were measured for both the quasi-static and acoustic stimulus frequencies. In the frequency range of 0.3-4 kHz, we used electromagnetic stimulation of the ossicle and a laser Doppler vibrometer to measure the vibration response. At low frequencies, harmonic displacements were imposed on the columella using piezo stimulation and the resulting force response was measured with a force sensor. From these measurement data, the acoustic impedance of the inner ear could be determined. A simple RLC model in series of the impedance measurements resulted in a stiffness reactance of KIE = 0.20·10¹² Pa/m³, an inertial impedance of MIE = 0.652·10⁶ Pa·s²/m³, and a resistance of RIE = 1.57·10⁹ Pa·s/m. We found that values of the inner ear impedance in the ostrich are one to two orders in magnitude smaller than what is found in mammal ears.



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Cortical reorganization in postlingually deaf cochlear implant users: intra-modal and cross-modal considerations

Publication date: Available online 26 July 2016
Source:Hearing Research
Author(s): Maren Stropahl, Ling-Chia Chen, Stefan Debener
With the advances of cochlear implant (CI) technology, many deaf individuals can partially regain their hearing ability. However, there is a large variation in the level of recovery. Cortical changes induced by hearing deprivation and restoration with CIs have been thought to contribute to this variation. The current review aims to identify these cortical changes in postlingually deaf CI users and discusses their maladaptive or adaptive relationship to the CI outcome. Overall, intra-modal and cross-modal reorganization patterns have been identified in postlingually deaf CI users in visual and in auditory cortex. Even though cross-modal activation in auditory cortex is considered as maladaptive for speech recovery in CI users, a similar activation relates positively to lip reading skills. Furthermore, cross-modal activation of the visual cortex seems to be adaptive for speech recognition. Currently available evidence points to an involvement of further brain areas and suggests that a focus on the reversal of visual take-over of the auditory cortex may be too limited. Future investigations should consider expanded cortical as well as multi-sensory processing and capture different hierarchical processing steps. Furthermore, prospective longitudinal designs are needed to track the dynamics of cortical plasticity that takes place before and after implantation.



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Atypical white-matter microstructure in congenitally deaf adults: a region of interest and tractography study using diffusion-tensor imaging

Publication date: Available online 26 July 2016
Source:Hearing Research
Author(s): Christina M. Karns, Courtney Stevens, Mark W. Dow, Emily Schorr, Helen J. Neville
Considerable research documents the cross-modal reorganization of auditory cortices as a consequence of congenital deafness, with remapped functions that include visual and somatosensory processing of both linguistic and nonlinguistic information. Structural changes accompany this cross-modal neuroplasticity, but precisely which specific structural changes accompany congenital and early deafness and whether there are group differences in hemispheric asymmetries remain to be established. Here, we used diffusion tensor imaging (DTI) to examine microstructural white matter changes accompanying cross-modal reorganization in 23 deaf adults who were genetically, profoundly, and congenitally deaf, having learned sign language from infancy with 26 hearing controls who participated in our previous fMRI studies of cross-modal neuroplasticity. In contrast to prior literature using a whole-brain approach, we introduce a semiautomatic method for demarcating auditory regions in which regions of interest (ROIs) are defined on the normalized white matter skeleton for all participants, projected into each participants native space, and manually constrained to anatomical boundaries. White-matter ROIs were left and right Heschl’s gyrus (HG), left and right anterior superior temporal gyrus (aSTG), left and right posterior superior temporal gyrus (pSTG), as well as one tractography-defined region in the splenium of the corpus callosum connecting homologous left and right superior temporal regions (pCC). Within these regions, we measured fractional anisotropy (FA), radial diffusivity (RD), axial diffusivity (AD), and white-matter volume. Congenitally deaf adults had reduced FA and volume in white matter structures underlying bilateral HG, aSTG, pSTG, and reduced FA in pCC. In HG and pCC, this reduction in FA corresponded with increased RD, but differences in aSTG and pSTG could not be localized to alterations in RD or AD. Direct statistical tests of hemispheric asymmetries in these differences indicated the most prominent effects in pSTG, where the largest differences between groups occurred in the right hemisphere. Other regions did not show significant hemispheric asymmetries in group differences. Taken together, these results indicate that atypical white matter microstructure and reduced volume underlies regions of superior temporal primary and association auditory cortex and introduce a robust method for quantifying volumetric and white matter microstructural differences that can be applied to future studies of special populations.



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Plasticity in bilateral superior temporal cortex: effects of deafness and cochlear implantation on auditory and visual speech processing

Publication date: Available online 26 July 2016
Source:Hearing Research
Author(s): Carly A. Anderson, Diane S. Lazard, Douglas EH. Hartley
While many individuals can benefit substantially from cochlear implantation, the ability to perceive and understand auditory speech with a cochlear implant (CI) remains highly variable amongst adult recipients. Importantly, auditory performance with a CI cannot be reliably predicted based solely on routinely obtained information regarding clinical characteristics of the CI candidate. This review argues that central factors, notably cortical function and plasticity, should also be considered as important contributors to the observed individual variability in CI outcome. Superior temporal cortex (STC), including auditory association areas, plays a crucial role in the processing of auditory and visual speech information. The current review considers evidence of cortical plasticity within bilateral STC, and how these effects may explain variability in CI outcome. Furthermore, evidence of audio-visual interactions in temporal and occipital cortices is examined, and relation to CI outcome is discussed. To date, longitudinal examination of changes in cortical function and plasticity over the period of rehabilitation with a CI has been restricted by methodological challenges. The application of functional near-infrared spectroscopy (fNIRS) in studying cortical function in CI users is becoming increasingly recognised as a potential solution to these problems. Here we suggest that fNIRS offers a powerful neuroimaging tool to elucidate the relationship between audio-visual interactions, cortical plasticity during deafness and following cochlear implantation, and individual variability in auditory performance with a CI.



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The effect of progressive hearing loss on the morphology of endbulbs of Held and bushy cells

Publication date: Available online 26 July 2016
Source:Hearing Research
Author(s): Catherine J. Connelly, David K. Ryugo, Michael A. Muniak
Studies of congenital and early-onset deafness have demonstrated that an absence of peripheral sound-evoked activity in the auditory nerve causes pathological changes in central auditory structures. The aim of this study was to establish whether progressive acquired hearing loss could lead to similar brain changes that would degrade the precision of signal transmission. We used complementary physiologic hearing tests and microscopic techniques to study the combined effect of both magnitude and duration of hearing loss on one of the first auditory synapses in the brain, the endbulb of Held (EB), along with its bushy cell (BC) target in the anteroventral cochlear nucleus. We compared two hearing mouse strains (CBA/Ca and heterozygous shaker-2^+/-) against a model of early-onset progressive hearing loss (DBA/2) and a model of congenital deafness (homozygous shaker-2^-/-), examining each strain at 1, 3, and 6 months of age. Furthermore, we employed a frequency model of the mouse cochlear nucleus to constrain our analyses to regions most likely to exhibit graded changes in hearing function with time. No significant differences in the gross morphology of EB or BC structure were observed in 1-month-old animals, indicating uninterrupted development. However, in animals with hearing loss, both EBs and BCs exhibited a graded reduction in size that paralleled the hearing loss, with the most severe pathology seen in deaf 6-month-old shaker-2^-/- mice. Ultrastructural pathologies associated with hearing loss were less dramatic: minor changes were observed in terminal size but mitochondrial fraction and postsynaptic densities remained relatively stable. These results indicate that acquired progressive hearing loss can have consequences on auditory brain structure, with prolonged loss leading to greater pathologies. Our findings suggest a role for early intervention with assistive devices in order to mitigate long-term pathology and loss of function.



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via IFTTT

Seasonal variations in auditory processing in the inferior colliculus of Eptesicus fuscus

Publication date: Available online 26 July 2016
Source:Hearing Research
Author(s): Kimberly E. Miller, Kaitlyn Barr, Mitchell Krawczyk, Ellen Covey
Eptesicus fuscus is typical of temperate zone bats in that both sexes undergo marked seasonal changes in behavior, endocrine status, and reproductive status. Acoustic communication plays a key role in many seasonal behaviors. For example, males emit specialized vocalizations during mating in the fall, and females use different specialized vocalizations to communicate with infants in late spring. Bats of both sexes use echolocation for foraging during times of activity, but engage in little sound-directed behavior during torpor and hibernation in winter. Auditory processing might be expected to reflect these marked seasonal changes.To explore the possibility that seasonal changes in hormonal status could drive functional plasticity in the central auditory system, we examined responses of single neurons in the inferior colliculus throughout the year.The average first-spike latency in females varied seasonally, almost doubling in spring compared to other times of year. First-spike latencies in males remained relatively stable throughout the year. Latency jitter for both sexes was higher in winter and spring than in summer or fall.Females had more burst responders than other discharge patterns throughout the year whereas males had more transient responders at all times of year except fall, when burst responses were the predominant type. The percentage of simple discharge patterns (sustained and transient) was higher in males than females in the spring and higher in females than males in the fall.In females, the percentage of shortpass duration-tuned neurons doubled in summer and remained elevated through fall and early winter. In males, the percentage of shortpass duration-tuned cells increased in spring and the percentage of bandpass duration-tuned cells doubled in the fall.These findings suggest that there are clear seasonal changes in basic response characteristics of midbrain auditory neurons in Eptesicus, especially in temporal response properties and duration sensitivity. Moreover, the pattern of changes is different in males and females, suggesting that hormone-driven plasticity adjusts central auditory processing to fit the characteristics of vocalizations specific to seasonal behavioral patterns.



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via IFTTT

Acoustic input impedance of the avian inner ear measured in ostrich (Struthio camelus)

Publication date: Available online 26 July 2016
Source:Hearing Research
Author(s): Pieter G.G. Muyshondt, Peter Aerts, Joris J.J. Dirckx
In both mammals and birds, the mechanical behavior of the middle ear structures is affected by the mechanical impedance of the inner ear. In this study, the aim was to quantify the acoustic impedance of the avian inner ear in the ostrich, which allows us to determine the effect on columellar vibrations and middle ear power flow in future studies. To determine the inner ear impedance, vibrations of the columella were measured for both the quasi-static and acoustic stimulus frequencies. In the frequency range of 0.3-4 kHz, we used electromagnetic stimulation of the ossicle and a laser Doppler vibrometer to measure the vibration response. At low frequencies, harmonic displacements were imposed on the columella using piezo stimulation and the resulting force response was measured with a force sensor. From these measurement data, the acoustic impedance of the inner ear could be determined. A simple RLC model in series of the impedance measurements resulted in a stiffness reactance of KIE = 0.20·10¹² Pa/m³, an inertial impedance of MIE = 0.652·10⁶ Pa·s²/m³, and a resistance of RIE = 1.57·10⁹ Pa·s/m. We found that values of the inner ear impedance in the ostrich are one to two orders in magnitude smaller than what is found in mammal ears.



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via IFTTT

Cortical reorganization in postlingually deaf cochlear implant users: intra-modal and cross-modal considerations

Publication date: Available online 26 July 2016
Source:Hearing Research
Author(s): Maren Stropahl, Ling-Chia Chen, Stefan Debener
With the advances of cochlear implant (CI) technology, many deaf individuals can partially regain their hearing ability. However, there is a large variation in the level of recovery. Cortical changes induced by hearing deprivation and restoration with CIs have been thought to contribute to this variation. The current review aims to identify these cortical changes in postlingually deaf CI users and discusses their maladaptive or adaptive relationship to the CI outcome. Overall, intra-modal and cross-modal reorganization patterns have been identified in postlingually deaf CI users in visual and in auditory cortex. Even though cross-modal activation in auditory cortex is considered as maladaptive for speech recovery in CI users, a similar activation relates positively to lip reading skills. Furthermore, cross-modal activation of the visual cortex seems to be adaptive for speech recognition. Currently available evidence points to an involvement of further brain areas and suggests that a focus on the reversal of visual take-over of the auditory cortex may be too limited. Future investigations should consider expanded cortical as well as multi-sensory processing and capture different hierarchical processing steps. Furthermore, prospective longitudinal designs are needed to track the dynamics of cortical plasticity that takes place before and after implantation.



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via IFTTT

Atypical white-matter microstructure in congenitally deaf adults: a region of interest and tractography study using diffusion-tensor imaging

Publication date: Available online 26 July 2016
Source:Hearing Research
Author(s): Christina M. Karns, Courtney Stevens, Mark W. Dow, Emily Schorr, Helen J. Neville
Considerable research documents the cross-modal reorganization of auditory cortices as a consequence of congenital deafness, with remapped functions that include visual and somatosensory processing of both linguistic and nonlinguistic information. Structural changes accompany this cross-modal neuroplasticity, but precisely which specific structural changes accompany congenital and early deafness and whether there are group differences in hemispheric asymmetries remain to be established. Here, we used diffusion tensor imaging (DTI) to examine microstructural white matter changes accompanying cross-modal reorganization in 23 deaf adults who were genetically, profoundly, and congenitally deaf, having learned sign language from infancy with 26 hearing controls who participated in our previous fMRI studies of cross-modal neuroplasticity. In contrast to prior literature using a whole-brain approach, we introduce a semiautomatic method for demarcating auditory regions in which regions of interest (ROIs) are defined on the normalized white matter skeleton for all participants, projected into each participants native space, and manually constrained to anatomical boundaries. White-matter ROIs were left and right Heschl’s gyrus (HG), left and right anterior superior temporal gyrus (aSTG), left and right posterior superior temporal gyrus (pSTG), as well as one tractography-defined region in the splenium of the corpus callosum connecting homologous left and right superior temporal regions (pCC). Within these regions, we measured fractional anisotropy (FA), radial diffusivity (RD), axial diffusivity (AD), and white-matter volume. Congenitally deaf adults had reduced FA and volume in white matter structures underlying bilateral HG, aSTG, pSTG, and reduced FA in pCC. In HG and pCC, this reduction in FA corresponded with increased RD, but differences in aSTG and pSTG could not be localized to alterations in RD or AD. Direct statistical tests of hemispheric asymmetries in these differences indicated the most prominent effects in pSTG, where the largest differences between groups occurred in the right hemisphere. Other regions did not show significant hemispheric asymmetries in group differences. Taken together, these results indicate that atypical white matter microstructure and reduced volume underlies regions of superior temporal primary and association auditory cortex and introduce a robust method for quantifying volumetric and white matter microstructural differences that can be applied to future studies of special populations.



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via IFTTT

Plasticity in bilateral superior temporal cortex: effects of deafness and cochlear implantation on auditory and visual speech processing

Publication date: Available online 26 July 2016
Source:Hearing Research
Author(s): Carly A. Anderson, Diane S. Lazard, Douglas EH. Hartley
While many individuals can benefit substantially from cochlear implantation, the ability to perceive and understand auditory speech with a cochlear implant (CI) remains highly variable amongst adult recipients. Importantly, auditory performance with a CI cannot be reliably predicted based solely on routinely obtained information regarding clinical characteristics of the CI candidate. This review argues that central factors, notably cortical function and plasticity, should also be considered as important contributors to the observed individual variability in CI outcome. Superior temporal cortex (STC), including auditory association areas, plays a crucial role in the processing of auditory and visual speech information. The current review considers evidence of cortical plasticity within bilateral STC, and how these effects may explain variability in CI outcome. Furthermore, evidence of audio-visual interactions in temporal and occipital cortices is examined, and relation to CI outcome is discussed. To date, longitudinal examination of changes in cortical function and plasticity over the period of rehabilitation with a CI has been restricted by methodological challenges. The application of functional near-infrared spectroscopy (fNIRS) in studying cortical function in CI users is becoming increasingly recognised as a potential solution to these problems. Here we suggest that fNIRS offers a powerful neuroimaging tool to elucidate the relationship between audio-visual interactions, cortical plasticity during deafness and following cochlear implantation, and individual variability in auditory performance with a CI.



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via IFTTT

The effect of progressive hearing loss on the morphology of endbulbs of Held and bushy cells

Publication date: Available online 26 July 2016
Source:Hearing Research
Author(s): Catherine J. Connelly, David K. Ryugo, Michael A. Muniak
Studies of congenital and early-onset deafness have demonstrated that an absence of peripheral sound-evoked activity in the auditory nerve causes pathological changes in central auditory structures. The aim of this study was to establish whether progressive acquired hearing loss could lead to similar brain changes that would degrade the precision of signal transmission. We used complementary physiologic hearing tests and microscopic techniques to study the combined effect of both magnitude and duration of hearing loss on one of the first auditory synapses in the brain, the endbulb of Held (EB), along with its bushy cell (BC) target in the anteroventral cochlear nucleus. We compared two hearing mouse strains (CBA/Ca and heterozygous shaker-2^+/-) against a model of early-onset progressive hearing loss (DBA/2) and a model of congenital deafness (homozygous shaker-2^-/-), examining each strain at 1, 3, and 6 months of age. Furthermore, we employed a frequency model of the mouse cochlear nucleus to constrain our analyses to regions most likely to exhibit graded changes in hearing function with time. No significant differences in the gross morphology of EB or BC structure were observed in 1-month-old animals, indicating uninterrupted development. However, in animals with hearing loss, both EBs and BCs exhibited a graded reduction in size that paralleled the hearing loss, with the most severe pathology seen in deaf 6-month-old shaker-2^-/- mice. Ultrastructural pathologies associated with hearing loss were less dramatic: minor changes were observed in terminal size but mitochondrial fraction and postsynaptic densities remained relatively stable. These results indicate that acquired progressive hearing loss can have consequences on auditory brain structure, with prolonged loss leading to greater pathologies. Our findings suggest a role for early intervention with assistive devices in order to mitigate long-term pathology and loss of function.



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via IFTTT

Seasonal variations in auditory processing in the inferior colliculus of Eptesicus fuscus

Publication date: Available online 26 July 2016
Source:Hearing Research
Author(s): Kimberly E. Miller, Kaitlyn Barr, Mitchell Krawczyk, Ellen Covey
Eptesicus fuscus is typical of temperate zone bats in that both sexes undergo marked seasonal changes in behavior, endocrine status, and reproductive status. Acoustic communication plays a key role in many seasonal behaviors. For example, males emit specialized vocalizations during mating in the fall, and females use different specialized vocalizations to communicate with infants in late spring. Bats of both sexes use echolocation for foraging during times of activity, but engage in little sound-directed behavior during torpor and hibernation in winter. Auditory processing might be expected to reflect these marked seasonal changes.To explore the possibility that seasonal changes in hormonal status could drive functional plasticity in the central auditory system, we examined responses of single neurons in the inferior colliculus throughout the year.The average first-spike latency in females varied seasonally, almost doubling in spring compared to other times of year. First-spike latencies in males remained relatively stable throughout the year. Latency jitter for both sexes was higher in winter and spring than in summer or fall.Females had more burst responders than other discharge patterns throughout the year whereas males had more transient responders at all times of year except fall, when burst responses were the predominant type. The percentage of simple discharge patterns (sustained and transient) was higher in males than females in the spring and higher in females than males in the fall.In females, the percentage of shortpass duration-tuned neurons doubled in summer and remained elevated through fall and early winter. In males, the percentage of shortpass duration-tuned cells increased in spring and the percentage of bandpass duration-tuned cells doubled in the fall.These findings suggest that there are clear seasonal changes in basic response characteristics of midbrain auditory neurons in Eptesicus, especially in temporal response properties and duration sensitivity. Moreover, the pattern of changes is different in males and females, suggesting that hormone-driven plasticity adjusts central auditory processing to fit the characteristics of vocalizations specific to seasonal behavioral patterns.



from #Audiology via ola Kala on Inoreader http://ift.tt/29YVEao
via IFTTT

Acoustic input impedance of the avian inner ear measured in ostrich (Struthio camelus)

Publication date: Available online 26 July 2016
Source:Hearing Research
Author(s): Pieter G.G. Muyshondt, Peter Aerts, Joris J.J. Dirckx
In both mammals and birds, the mechanical behavior of the middle ear structures is affected by the mechanical impedance of the inner ear. In this study, the aim was to quantify the acoustic impedance of the avian inner ear in the ostrich, which allows us to determine the effect on columellar vibrations and middle ear power flow in future studies. To determine the inner ear impedance, vibrations of the columella were measured for both the quasi-static and acoustic stimulus frequencies. In the frequency range of 0.3-4 kHz, we used electromagnetic stimulation of the ossicle and a laser Doppler vibrometer to measure the vibration response. At low frequencies, harmonic displacements were imposed on the columella using piezo stimulation and the resulting force response was measured with a force sensor. From these measurement data, the acoustic impedance of the inner ear could be determined. A simple RLC model in series of the impedance measurements resulted in a stiffness reactance of KIE = 0.20·10¹² Pa/m³, an inertial impedance of MIE = 0.652·10⁶ Pa·s²/m³, and a resistance of RIE = 1.57·10⁹ Pa·s/m. We found that values of the inner ear impedance in the ostrich are one to two orders in magnitude smaller than what is found in mammal ears.



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via IFTTT

Cortical reorganization in postlingually deaf cochlear implant users: intra-modal and cross-modal considerations

Publication date: Available online 26 July 2016
Source:Hearing Research
Author(s): Maren Stropahl, Ling-Chia Chen, Stefan Debener
With the advances of cochlear implant (CI) technology, many deaf individuals can partially regain their hearing ability. However, there is a large variation in the level of recovery. Cortical changes induced by hearing deprivation and restoration with CIs have been thought to contribute to this variation. The current review aims to identify these cortical changes in postlingually deaf CI users and discusses their maladaptive or adaptive relationship to the CI outcome. Overall, intra-modal and cross-modal reorganization patterns have been identified in postlingually deaf CI users in visual and in auditory cortex. Even though cross-modal activation in auditory cortex is considered as maladaptive for speech recovery in CI users, a similar activation relates positively to lip reading skills. Furthermore, cross-modal activation of the visual cortex seems to be adaptive for speech recognition. Currently available evidence points to an involvement of further brain areas and suggests that a focus on the reversal of visual take-over of the auditory cortex may be too limited. Future investigations should consider expanded cortical as well as multi-sensory processing and capture different hierarchical processing steps. Furthermore, prospective longitudinal designs are needed to track the dynamics of cortical plasticity that takes place before and after implantation.



from #Audiology via ola Kala on Inoreader http://ift.tt/29YWkMS
via IFTTT

Atypical white-matter microstructure in congenitally deaf adults: a region of interest and tractography study using diffusion-tensor imaging

Publication date: Available online 26 July 2016
Source:Hearing Research
Author(s): Christina M. Karns, Courtney Stevens, Mark W. Dow, Emily Schorr, Helen J. Neville
Considerable research documents the cross-modal reorganization of auditory cortices as a consequence of congenital deafness, with remapped functions that include visual and somatosensory processing of both linguistic and nonlinguistic information. Structural changes accompany this cross-modal neuroplasticity, but precisely which specific structural changes accompany congenital and early deafness and whether there are group differences in hemispheric asymmetries remain to be established. Here, we used diffusion tensor imaging (DTI) to examine microstructural white matter changes accompanying cross-modal reorganization in 23 deaf adults who were genetically, profoundly, and congenitally deaf, having learned sign language from infancy with 26 hearing controls who participated in our previous fMRI studies of cross-modal neuroplasticity. In contrast to prior literature using a whole-brain approach, we introduce a semiautomatic method for demarcating auditory regions in which regions of interest (ROIs) are defined on the normalized white matter skeleton for all participants, projected into each participants native space, and manually constrained to anatomical boundaries. White-matter ROIs were left and right Heschl’s gyrus (HG), left and right anterior superior temporal gyrus (aSTG), left and right posterior superior temporal gyrus (pSTG), as well as one tractography-defined region in the splenium of the corpus callosum connecting homologous left and right superior temporal regions (pCC). Within these regions, we measured fractional anisotropy (FA), radial diffusivity (RD), axial diffusivity (AD), and white-matter volume. Congenitally deaf adults had reduced FA and volume in white matter structures underlying bilateral HG, aSTG, pSTG, and reduced FA in pCC. In HG and pCC, this reduction in FA corresponded with increased RD, but differences in aSTG and pSTG could not be localized to alterations in RD or AD. Direct statistical tests of hemispheric asymmetries in these differences indicated the most prominent effects in pSTG, where the largest differences between groups occurred in the right hemisphere. Other regions did not show significant hemispheric asymmetries in group differences. Taken together, these results indicate that atypical white matter microstructure and reduced volume underlies regions of superior temporal primary and association auditory cortex and introduce a robust method for quantifying volumetric and white matter microstructural differences that can be applied to future studies of special populations.



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via IFTTT

Plasticity in bilateral superior temporal cortex: effects of deafness and cochlear implantation on auditory and visual speech processing

Publication date: Available online 26 July 2016
Source:Hearing Research
Author(s): Carly A. Anderson, Diane S. Lazard, Douglas EH. Hartley
While many individuals can benefit substantially from cochlear implantation, the ability to perceive and understand auditory speech with a cochlear implant (CI) remains highly variable amongst adult recipients. Importantly, auditory performance with a CI cannot be reliably predicted based solely on routinely obtained information regarding clinical characteristics of the CI candidate. This review argues that central factors, notably cortical function and plasticity, should also be considered as important contributors to the observed individual variability in CI outcome. Superior temporal cortex (STC), including auditory association areas, plays a crucial role in the processing of auditory and visual speech information. The current review considers evidence of cortical plasticity within bilateral STC, and how these effects may explain variability in CI outcome. Furthermore, evidence of audio-visual interactions in temporal and occipital cortices is examined, and relation to CI outcome is discussed. To date, longitudinal examination of changes in cortical function and plasticity over the period of rehabilitation with a CI has been restricted by methodological challenges. The application of functional near-infrared spectroscopy (fNIRS) in studying cortical function in CI users is becoming increasingly recognised as a potential solution to these problems. Here we suggest that fNIRS offers a powerful neuroimaging tool to elucidate the relationship between audio-visual interactions, cortical plasticity during deafness and following cochlear implantation, and individual variability in auditory performance with a CI.



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The effect of progressive hearing loss on the morphology of endbulbs of Held and bushy cells

Publication date: Available online 26 July 2016
Source:Hearing Research
Author(s): Catherine J. Connelly, David K. Ryugo, Michael A. Muniak
Studies of congenital and early-onset deafness have demonstrated that an absence of peripheral sound-evoked activity in the auditory nerve causes pathological changes in central auditory structures. The aim of this study was to establish whether progressive acquired hearing loss could lead to similar brain changes that would degrade the precision of signal transmission. We used complementary physiologic hearing tests and microscopic techniques to study the combined effect of both magnitude and duration of hearing loss on one of the first auditory synapses in the brain, the endbulb of Held (EB), along with its bushy cell (BC) target in the anteroventral cochlear nucleus. We compared two hearing mouse strains (CBA/Ca and heterozygous shaker-2^+/-) against a model of early-onset progressive hearing loss (DBA/2) and a model of congenital deafness (homozygous shaker-2^-/-), examining each strain at 1, 3, and 6 months of age. Furthermore, we employed a frequency model of the mouse cochlear nucleus to constrain our analyses to regions most likely to exhibit graded changes in hearing function with time. No significant differences in the gross morphology of EB or BC structure were observed in 1-month-old animals, indicating uninterrupted development. However, in animals with hearing loss, both EBs and BCs exhibited a graded reduction in size that paralleled the hearing loss, with the most severe pathology seen in deaf 6-month-old shaker-2^-/- mice. Ultrastructural pathologies associated with hearing loss were less dramatic: minor changes were observed in terminal size but mitochondrial fraction and postsynaptic densities remained relatively stable. These results indicate that acquired progressive hearing loss can have consequences on auditory brain structure, with prolonged loss leading to greater pathologies. Our findings suggest a role for early intervention with assistive devices in order to mitigate long-term pathology and loss of function.



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