Plasticity in the adult human central auditory system: evidence from late-onset profound unilateral deafness.

Experience-related changes in central nervous system (CNS) activity have been observed in the adult brain of many mammalian species, including humans. In humans, late-onset profound unilateral deafness creates an opportunity to study plasticity in the adult CNS consequent to monaural auditory deprivation. CNS activity was assessed by measuring long-latency auditory evoked potentials (AEPs) recorded from teens and adults with late-onset (post-childhood) profound unilateral deafness. Compared to monaurally stimulated normal-hearing subjects, the AEPs recorded from central electrode sites located over auditory cortical areas showed significant increases in inter-hemispheric waveform cross-correlation coefficients, and in inter-hemispheric AEP peak amplitude correlations. These increases provide evidence of substantial changes from the normal pattern of asymmetrical (contralateral > ipsilateral amplitude) and asynchronous (contralateral earlier than ipsilateral) central auditory system activation in the normal-hearing population to a much more symmetrical and synchronous activation in the unilaterally deaf. These cross-sectional analyses of AEP data recorded from the unilaterally deaf also suggest that the changes in cortical activity occur gradually and continue for at least 2 years after the onset of hearing loss. Analyses of peak amplitude correlations suggest that the increased inter-hemispheric symmetry may be a consequence of changes in the generators producing the N (approximately 100 ms peak latency) potential. These experience-related changes in central auditory system activity following late-onset profound unilateral deafness thus provide evidence of the presence and the time course of auditory system plasticity in the adult brain.     

Sudden deafness: long-term follow-up and recurrence

We examined the long-term outcome for patients with idiopathic sudden sensorineural hearing loss (sudden deafness), including the incidence of recurrence of sudden deafness. The subjects were 1,798 individuals who came to Nagoya University hospital within 2 weeks of the onset of unilateral sudden deafness. Only 14 of the patients had a history of being diagnosed with sudden deafness. After their visit to our hospital, one patient had a recurrence in the ipsilateral ear and four patients experienced sudden deafness in the contralateral ear. We performed hearing examinations on 88 patients who revisited our hospital more than 10 years after unilateral sudden deafness. Of these patients, there was one with a recurrence in the ipsilateral ear and one with sudden deafness in the contralateral ear. Thus, in this series the recurrence of sudden deafness was rare.     

Sudden deafness: long‐term follow‐up and recurrence

We examined the long‐term outcome for patients with idiopathic sudden sensorineural hearing loss (sudden deafness), including the incidence of recurrence of sudden deafness. The subjects were 1798 individuals who came to Nagoya University hospital within 2 weeks of the onset of unilateral sudden deafness. Only 14 of the patients had a history of being diagnosed with sudden deafness. After their visit to our hospital, one patient had a recurrence in the ipsilateral ear and four patients experienced sudden deafness in the contralateral ear. We performed hearing examinations on 88 patients who revisited our hospital more than 10 years after unilateral sudden deafness. Of these patients, there was one with a recurrence in the ipsilateral ear and one with sudden deafness in the contralateral ear. Thus, in this series the recurrence of sudden deafness was rare.     

Delayed endolymphatic hydrops as a clinical entity

Delayed endolymphatic hydrops (DEH) is a clinical entity that can be differentiated from Ménière's disease and is typically observed in patients who have been suffering from longstanding unilateral profound inner-ear hearing loss. DEH probably is caused by delayed atrophy or fibrous obliteration of the endolymphatic resorptive system of the membranous labyrinth. The time that elapses between the occurrence of hearing loss and the onset of DEH can range from 1 to 74 years. The most common cause of hearing loss preceding DEH is juvenile-onset unilateral profound deafness (early childhood unilateral profound sensorineural hearing loss of unknown etiology), followed by labyrinthitis from various causes and physical and acoustic traumas to the inner ear. Two types of DEH exist: the ipsilateral type, in which the ear with profound hearing loss suffers progressive endolymphatic hydrops, and the contralateral type, in which the formation of progressive endolymphatic hydrops takes place in the ear opposite to the previously deafened ear. The incidence of the ipsilateral type is higher than that of the contralateral type, and the contralateral type is more common in older patients. When recurrent episodic vertigo cannot be remedied through conservative treatment, labyrinthectomy and vestibular neurectomy on the deaf ear are curative for ipsilateral DEH. However, no such surgical treatment is available for the contralateral type.     

ABR in multiple sclerosis. Ipsi- versus contralateral derivation

Brainstem auditory evoked potentials (ABR) were recorded simultaneously between vertex and ear lobe, ipsi- and contralateral to the stimulated ear in 53 subjects with confirmed (19) or undefined (34) multiple sclerosis. Results were compared with those obtained in a control group of 20 normal-hearing adults. The control group showed that significant latency differences exist between ipsilateral and contralateral recordings. Definition of abnormality was based on absence and separation of waves. The results showed that the use of contralateral derivation in ABR recordings increased detectability from 74% to 89% in patients with confirmed MS and from 9% to 21% in cases of undefined MS. It is proposed that parameters of contralateral ABRs be included among the criteria used for the otoneurological diagnosis of patients with CNS lesions.     

Functional brain imaging as an objective measure of speech perception performance in adult cochlear implant users

In this study we examined the role of functional brain imaging of regional cerebral bloodflow (rCBF) with the use of single photon emission computed tomography (SPECT) for the objective measurement of brain performance in adult cochlear implant (CI) users during speech perception. The subjects consisted of nine normal-hearing and eight CI individuals who watched a 15-min videotape under two conditions: (1) a visual-only presentation; and (2) a left-monaural audio and visual presentation. Cortical activations were observed bilaterally in Brodmann areas 41, 42, 21, 22 and 38 for normal-hearing control subjects. Bilateral activations were also observed in CI individuals who demonstrated high performance on open-set speech recognition tasks; however, activations were smaller in both amplitude and extent than those observed for normal-hearing individuals. CI individuals with minimal open-set recognition demonstrated only unilateral activation of auditory cortex in the hemisphere contralateral to the ear of implantation. These data support SPECT as a tool for objectively documenting cortical activations in adult CI users.     

Auditory brain stem response in newborn infants--masking effect on ipsi- and contralateral recording

Ipsilateral and contralateral auditory brain stem responses (ABR) were recorded in 10 full-term neonates. We investigated the effect of the masking level on the peak latency and amplitude on ipsi- and contralateral recordings. Clicks were presented at 85 dB HL to the ipsilateral ear and the masking white noise was presented at 75, 65, 55, 45 and 0 dB HL on the contralateral one, respectively. Masking had no significant effect on the ipsi- and contralateral recording in regard to latency and amplitude except for wave CVI (contralateral wave VI). In addition, ABR was recorded in an infant with total unilateral hearing loss. Crossover responses on both sides were observed with-out contralateral masking, but these responses were completely eliminated when 45 dB HL contralateral masking masked the 85 dB HL clicks to the dead ear. Therefore, it is suggested that such crossover responses will contribute to the ipsi- and contralaterally recorded ABR waveform when an ABR recording is carried out without contralateral masking. Our results indicate that contralateral masking is necessary and should be used in cases of unilateral hearing loss.     

Normal ipsilateral/contralateral asymmetries in infant multiple auditory steady-state responses to air- and bone-conduction stimuli

OBJECTIVES: Two-channel recordings of infants' air- and bone-conduction auditory brainstem responses to brief tones show ipsilateral and contralateral (to the stimulated ear) asymmetries which may be used to isolate which cochlea is the primary contributor to the response. The objective of this study was to determine whether similar ipsilateral/contralateral asymmetries are also present in the air- and bone-conduction "brainstem" (77 to 101 Hz) auditory steady-state responses (ASSRs) of infants. DESIGN: Two-channel ASSRs were recorded in infants (2 to 11 mo) and adults (18 to 40 yr) with normal hearing. Multiple stimuli (carrier frequencies: 500 to 4000 Hz; amplitude/frequency modulated) were presented using a B-71 oscillator on the temporal bone or an ER3-A insert earphone. Bone-conduction ASSR amplitudes, phase delays, and thresholds were obtained for the electroencephalographic (EEG) channels ipsilateral and contralateral to the oscillator temporal-bone placement. Bone-conduction ASSRs were also obtained to the stimulus presented to the opposite temporal bone (at 40 dB HL only). Air-conduction ASSR amplitudes and phase delays were obtained at 60 dB HL in each ear for the EEG channels ipsilateral and contralateral to the transducer. RESULTS: Infants showed more ipsilateral/contralateral asymmetries in both air- and bone-conduction ASSRs compared with adults. Mean bone-conduction ASSR thresholds in infants were 13 to 15 dB higher (i.e., poorer) in the contralateral EEG channel compared with the ipsilateral EEG channel for 500 to 4000 Hz. In adults, there were no large differences (i.e., within 1 dB) between ipsilateral and contralateral ASSR thresholds. Based on ipsilateral/ contralateral threshold differences in infants, interaural attenuation for bone-conducted stimuli was estimated to be at least 10 to 30 dB for most infants. In contrast, most adults showed little interaural attenuation for bone-conducted stimuli. ASSR amplitudes are larger and phase delays are shorter in the ipsilateral EEG channel. For infants, the difference in air-conduction ASSR amplitude between EEG channels was twice that observed for adults. Infants also had greater ASSR amplitude differences between EEG channels for bone-conduction stimuli compared with adults, but the difference was less than that seen for air-conduction stimuli. For air-conduction stimuli, infants had significantly longer phase delays in the contralateral EEG channel compared with the ipsilateral EEG channel. Adults showed no significant differences in air-conduction ASSR phase delay between EEG channels. For bone-conduction stimuli, both infants and adults had significantly longer phase delays in the contralateral EEG channel compared with the ipsilateral EEG channel; the differences in ASSR phase delays between EEG channels were much smaller in infants compared with adults and fewer adults had absent responses in the contralateral EEG channels compared with infants (12% versus 34%). When the transducers were switched to the opposite ear/mastoid, the infant and adult ipsilateral/contralateral asymmetries also switched. CONCLUSIONS: Ipsilateral/contralateral asymmetries in air- and bone-conduction ASSRs are clearly present more often and are larger in infants compared with adults. Our findings also suggest that most infants have at least 10 to 30 dB of interaural attenuation to bone-conducted stimuli. These asymmetries in the bone-conduction ASSR have potential as a clinical tool for isolating the cochlea that is contributing to the response in infants.     

N1 action potentials in humans: influence of simultaneous contralateral stimulation

Nl action potentials, elicited by low-level, 4.0-kHz filtered clicks, were recorded from the ear canals of normal-hearing adults. Responses were recorded at two sensation levels in the presence and absence of a pure tone delivered to the contralateral ear. Waveforms were analysed for changes in amplitude and latency. A significant reduction in the amplitude of Nl was observed following the introduction of the contralateral tone at both FC levels. A concomitant change in latency was not observed. For all subjects, ipsilateral and contralateral signals were below the intensities which resulted in acoustic reflexes and crossover of contralateral signals. These data suggest that the Nl amplitude reduction observed in this study represents inhibitory activity of the efferent auditory pathway.     

N1 action potentials in humans. Influence of simultaneous contralateral stimulation

N1 action potentials, elicited by low-level, 4.0-kHz filtered clicks, were recorded from the ear canals of normal-hearing adults. Responses were recorded at two sensation levels in the presence and absence of a pure tone delivered to the contralateral ear. Waveforms were analysed for changes in amplitude and latency. A significant reduction in the amplitude of N1 was observed following the introduction of the contralateral tone at both FC levels. A concomitant change in latency was not observed. For all subjects, ipsilateral and contralateral signals were below the intensities which resulted in acoustic reflexes and crossover of contralateral signals. These data suggest that the N1 amplitude reduction observed in this study represents inhibitory activity of the efferent auditory pathway.     

Delayed endolymphatic hydrops. Special emphasis on nystagmus associated with episodes and contribution of chemical labyrinthectomy

ObjectivesThe main objective was to describe spontaneous nystagmus characteristics during an episode of delayed endolymphatic hydrops (DEH), including an initial vertical upbeating nystagmus in one patient. The secondary objective was to highlight the contribution of chemical labyrinthectomy.MethodsEpisodic vertigo after a prolonged period of time of sensorineural hearing loss (profound or total) in one ear characterized ipsilateral DEH and was associated with the development of hearing loss in the opposite ear in contralateral DEH.ResultsTen patients met the criteria for DEH: 7 ipsilateral and 3 contralateral. Three (all ipsilateral DEH) were examined during a vertigo episode. Two patients had a typical horizontal-torsional nystagmus beating contralaterally to the hearing loss. One patient showed atypic initial vertical upbeating nystagmus with a slight torsional component, which secondarily became horizontal-torsional beating contralaterally to the hearing loss. Four patients had disabling vertigo with unilateral total deafness (ipsilateral DEH), successfully treated by 1-3 transtympanic gentamycin (Gentalline^®) injections.ConclusionNystagmus direction during vertigo episodes varies, and may initially present as vertical upbeating nystagmus, which, to our knowledge, has not been previously reported in DEH or Menière's disease. This nystagmus might reflect an inhibition of the superior semicircular canal (on the hearing-impaired side), suggesting incipient hydrops in this canal. Chemical labyrinthectomy is a simple and effective procedure in unilateral DEH, especially as the patient often suffers from total deafness.     

Suppression of evoked otoacoustic emissions by contralateral noise exposure in humans

The effects of contralateral noise exposure on evoked otoacoustic emission (e-OAE) were investigated in 10 normal hearing subjects and 3 cases with unilateral deafness. The e-OAE was recorded by ILO88 and weighting noise was given to the contralateral ear (impaired side in unilateral deafness cases). The air conducted noise exposure showed suppressive effect on e-OAE along with the increase of noise stimulus intensity in normal hearing subjects, but did not in unilateral deafness cases. The degree of suppression in e-OAE was most remarkable in highest peak power between 1 kHz and 2 kHz in FFT picture and the mean value of maximal suppression in 10 normal hearing subjects was 2.2 dB. The bone conducted noise exposure showed no effects on e-OAE in either normal hearing subjects or unilateral deafness cases. It was suggested that the contralateral noise exposure could suppress the function of cochlear micromechanics probably via crossed olivocochlear bundle.     

El implante coclear como tratamiento del acúfeno

Introduction and objectivesTinnitus is a symptom of high prevalence in patients with cochlear pathology. We studied the evolution of tinnitus in patients undergoing unilateral cochlear implantation for treatment of profound hearing loss.MethodsThis was a longitudinal, retrospective study of patients that underwent unilateral cochlear implantation and who had bilateral tinnitus. Tinnitus was assessed quantitatively and qualitatively before surgery and at 6 and 12 months after surgery.ResultsWe evaluated 20 patients that underwent unilateral cochlear implantation with a Nucleus^® CI24RE Contour Advance? electrode device. During the periods in which the device was in operation, improvement or disappearance of tinnitus was evidenced in the ipsilateral ear in 65% of patients, and in the contralateral ear, in 50%. In periods in which the device was disconnected, improvement or disappearance of tinnitus was found in the ipsilateral ear in 50% of patients, and in the ear contralateral to the implant in 45% of the patients. In 10% of the patients, a new tinnitus appeared in the ipsilateral ear.ConclusionsThe patients with profound hearing loss and bilateral tinnitus treated with unilateral cochlear implantation improved in a high percentage of cases, in the ipsilateral ear and in the contralateral ear.     

Clinical features in patients with delayed endolymphatic hydrops

We report clinical features in patients with delayed endolymphatic hydrops (DEH) with juvenile unilateral deafness. Among 23 patients with DEH, 15 cases were diagnosed as ipsilateral DEH and 8 cases as contralateral DEH. The distribution of onset age showed two peaks at ages of < 30 years and > 40 years. In 80% of the ipsilateral DEH cases, the onset of episodic vertigo was at younger ages. On the other hand, in 75% of the contralateral DEH cases, the onset of fluctuation hearing loss of the contralateral ear was at older ages. Ispilateral DEH and Meniere's disease may show different pathophysiologies. The incidence of dominant negative summating potential in the better-hearing ear was 20% in the ispilateral DEH cases and 60% in the contralateral DEH cases. It is suggested that endolymphatic hydrops is in the better-hearing ear of contralateral DEH.     

Presidential Speech

Conclusions. Patients with the contralateral type of delayed endolymphatic hydrops (DEH) may undergo an autoimmune attack against the other inner ear. As patients with unilateral juvenile deafness show no progression, despite lengthy observation, the autoantibody against the 68-kDa protein may be unrelated to the pathogenesis of DEH. Objective. The contralateral type of DEH is believed to have an autoimmune etiology, and sometimes develops from unilateral juvenile deafness. The purpose of this study was to determine whether autoantibodies are pathogenetically important in DEH. Material and methods. Sera from 9 patients with DEH, 18 patients with profound unilateral juvenile hearing loss and 15 control volunteer without inner ear diseases were investigated by means of Western blot assay against rat inner ear proteins. Results. Among 8 patients with the contralateral type of DEH, 6 (75%) showed at least 1 reactive band on Western blotting. The protein that reacted most frequently had a molecular weight of 28?kDa, which was consistent with our previous results. Among 18 patients with unilateral juvenile deafness, 5 (28%) showed reactive bands, exclusively at 68?kDa.     

Autoantibodies against inner ear proteins in patients with delayed endolymphatic hydrops and unilateral juvenile deafness

CONCLUSIONS: Patients with the contralateral type of delayed endolymphatic hydrops (DEH) may undergo an autoimmune attack against the other inner ear. As patients with unilateral juvenile deafness show no progression, despite lengthy observation, the autoantibody against the 68-kDa protein may be unrelated to the pathogenesis of DEH. OBJECTIVE: The contralateral type of DEH is believed to have an autoimmune etiology, and sometimes develops from unilateral juvenile deafness. The purpose of this study was to determine whether autoantibodies are pathogenetically important in DEH. MATERIAL AND METHODS: Sera from 9 patients with DEH, 18 patients with profound unilateral juvenile hearing loss and 15 control volunteer without inner ear diseases were investigated by means of Western blot assay against rat inner ear proteins. RESULTS: Among 8 patients with the contralateral type of DEH, 6 (75%) showed at least 1 reactive band on Western blotting. The protein that reacted most frequently had a molecular weight of 28 kDa, which was consistent with our previous results. Among 18 patients with unilateral juvenile deafness, 5 (28%) showed reactive bands, exclusively at 68 kDa.     

Study on tinnitus masking--an evaluation of ipsilateral and contralateral masking for tinnitus

In this study, the tinnitus masking curves measured by the ipsilateral and contralateral masking test were evaluated for the unilateral tinnitus cases of following 4 groups; 40 cases without hearing loss, 22 cases with symmetrical sensorineural hearing loss, 12 cases with unilateral deafness, and 70 cases with unilateral sensorineural hearing loss. Then the characteristics of tinnitus masking curves and central masking phenomenon for tinnitus masking were investigated. Consequently, tinnitus was masked by a masking tone given from nontinnitus ear when it reached at some definite loudness level, in spite of the presence of hearing loss or the degree of hearing loss in tinnitus ear. Then it was suggested to be a influence of central masking phenomenon in the contralateral tinnitus masking.     

Computed tomography demonstrates abnormalities of contralateral ear in subjects with unilateral sensorineural hearing loss

Purpose

Prior studies have associated gross inner ear abnormalities with pediatric sensorineural hearing loss (SNHL) using computed tomography (CT). No studies to date have specifically investigated morphologic inner ear abnormalities involving the contralateral unaffected ear in patients with unilateral SNHL. The purpose of this study is to evaluate contralateral inner ear structures of subjects with unilateral SNHL but no grossly abnormal findings on CT.

Materials and methods

IRB-approved retrospective analysis of pediatric temporal bone CT scans. 97 temporal bone CT scans, previously interpreted as “normal” based upon previously accepted guidelines by board certified neuroradiologists, were assessed using 12 measurements of the semicircular canals, cochlea and vestibule. The control-group consisted of 72 “normal” temporal bone CTs with underlying SNHL in the subject excluded. The study-group consisted of 25 normal-hearing contralateral temporal bones in subjects with unilateral SNHL. Multivariate analysis of covariance (MANCOVA) was then conducted to evaluate for differences between the study and control group.

Results

Cochlea basal turn lumen width was significantly greater in magnitude and central lucency of the lateral semicircular canal bony island was significantly lower in density for audiometrically normal ears of subjects with unilateral SNHL compared to controls.

Conclusion

Abnormalities of the inner ear were present in the contralateral audiometrically normal ears of subjects with unilateral SNHL. These data suggest that patients with unilateral SNHL may have a more pervasive disease process that results in abnormalities of both ears. The findings of a cochlea basal turn lumen width disparity >5% from “normal” and/or a lateral semicircular canal bony island central lucency disparity of >5% from “normal” may indicate inherent risk to the contralateral unaffected ear in pediatric patients with unilateral sensorineural hearing loss.     

听觉事件相关电位同侧与对侧记录的比较

目的 比较同侧与对侧听觉事件相关电位（auditory event-related potential,AWRP）的反应特性，探讨AERP在二侧听皮层发源上的神经电生理特点和机制及其临床意义。方法 选择正常青年人，采用同侧与对侧导联同时记录的方法记录AERP，分析二种记录条件下AERP各波潜伏期，幅值和波形的特性。结果 同侧与对侧记录的AERP在潜伏期和幅值上无显著性差异，但同侧记录的AERP波形明显优于对侧记录的曲线，表现为波形曲线光滑，波峰明显易辨，杂波成份少。结论 AERP在二侧听皮层的神经发源基本上是对称的，但同侧的反应怀明显优于对侧，可能与AERP的发源有部分皮层下成份的参与，听觉神经通路的双侧传导以及内侧橄榄耳蜗系统的对侧抑制效应有关，临床应用时应考虑到AERP发源部位和成份多元化的影响因素。     

Cochlear implantation in a child with posttraumatic single-sided deafness

Cochlear implantation has become a standard therapy for children with bilateral profound hearing loss, resulting in substantial and sustainable benefits for the development of expressive and receptive and expressive language skills and cognition. During the last few years, audiologic and otologic criteria for cochlear implantation have been expanded. Recently, patients with profound single-sided deafness with or without tinnitus have received cochlear implants despite normal to near-normal hearing on the contralateral side. This indication, however, has thus far been restricted to adult patients. Although it is known that unilateral hearing has an impact on social-emotional development in children, otologic surgeons have been reluctant to treat children with single-sided deafness with a cochlear implant. We report here on a case of successful cochlear implantation in an 8-year-old boy with acute single-sided deafness due to a lateral skull-base fracture, after an MRI showed signs of imminent fibrosis of the inner ear with possible prevention of cochlear implantation at a later stage. There was normal hearing in the contralateral ear. The child showed rapid development of speech discrimination in the implanted ear, improvements in sound localization and speech perception in noise, and a high degree of patient satisfaction. This experience may encourage using this therapeutic approach in children with chronic profound single-sided deafness.