Enhancement of phase-locking in rodents. I. An axonal recording study in gerbil.

The trapezoid body (TB) contains axons of neurons in the anteroventral cochlear nucleus projecting to monaural and binaural nuclei in the superior olivary complex (SOC). Characterization of these monaural inputs is important for the interpretation of response properties of SOC neurons. In particular, understanding of the sensitivity to interaural time differences (ITDs) in neurons of the medial and lateral superior olive requires knowledge of the temporal firing properties of the monaural excitatory and inhibitory inputs to these neurons. In recent years, studies of ITD sensitivity of SOC neurons have made increasing use of small animal models with good low-frequency hearing, particularly the gerbil. We presented stimuli as used in binaural studies to monaural neurons in the TB and studied their temporal coding. We found that general trends as have been described in the cat are present in gerbil, but with some important differences. Phase-locking to pure tones tends to be higher in TB axons and in neurons of the medial nucleus of the TB (MNTB) than in the auditory nerve for neurons with characteristic frequencies (CFs) below 1 kHz, but this enhancement is quantitatively more modest than in cat. Stronger enhancement is common when TB neurons are stimulated at low frequencies below CF. It is rare for TB neurons in gerbil to entrain to low-frequency stimuli, i.e., to discharge a well-timed spike on every stimulus cycle. Also, complex phase-locking behavior, with multiple modes of increased firing probability per stimulus cycle, is common in response to low frequencies below CF.NEW & NOTEWORTHY Phase-locking is an important property of neurons in the early auditory pathway: it is critical for the sensitivity to time differences between the two ears enabling spatial hearing. Studies in cat have shown an improvement in phase-locking from the peripheral to the central auditory nervous system. We recorded from axons in an output tract of the cochlear nucleus and show that a similar but more limited form of temporal enhancement is present in gerbil.

Axonal branching patterns as sources of delay in the mammalian auditory brainstem: a re-examination.

In models of temporal processing, time delays incurred by axonal propagation of action potentials play a prominent role. A pre-eminent model of temporal processing in audition is the binaural model of Jeffress (1948), which has dominated theories regarding our acute sensitivity to interaural time differences (ITDs). In Jeffress' model, a binaural cell is maximally active when the ITD is compensated by an internal delay, which brings the inputs from left and right ears in coincidence, and which would arise from axonal branching patterns of monaural input fibers. By arranging these patterns in systematic and opposite ways for the ipsilateral and contralateral inputs, a range of length differences, and thereby of internal delays, is created so that the ITD is transformed into a spatial activation pattern along the binaural nucleus. We reanalyze single, labeled, and physiologically characterized axons of spherical bushy cells of the cat anteroventral cochlear nucleus, which project to binaural coincidence detectors in the medial superior olive (MSO). The reconstructions largely confirm the observations of two previous reports, but several features are observed that are inconsistent with Jeffress' model. We found that ipsilateral projections can also form a caudally directed delay line pattern, which would counteract delays incurred by caudally directed contralateral projections. Comparisons of estimated axonal delays with binaural physiological data indicate that the suggestive anatomical patterns cannot account for the frequency-dependent distribution of best delays in the cat. Surprisingly, the tonotopic distribution of the afferent endings indicate that low characteristic frequencies are under-represented rather than over-represented in the MSO.

Cerebellar Ataxia as a Common Clinical Presentation Associated with DNMT1 p.Y511H and a Review of the Literature.

The phenotypes of patients with disease-associated variants in DNMT1 have been classified into two syndromes: hereditary sensory and autonomic neuropathy type 1E (HSAN1E, MIM614116, https://www.omim.org/ ) and autosomal dominant cerebellar ataxia, deafness, and narcolepsy (ADCA-DN, MIM604121). The amino acid codon 511 is a hotspot, and p.Y511C is the most frequently observed disease-associated variant among those in HSAN1E patients, whereas there have been only a few reports on patients with p.Y511H. In this study, we report on the cases of a kindred carrying the DNMT1 variant NM_001130823.2:c.1531 T > C (p.Y511H) presenting with the ADCA-DN phenotype. The review of the literature further revealed that later ages at onset and the presence of cerebellar ataxia are the main characteristics of patients carrying the DNMT1 p.Y511H as compared with those carrying DNMT1 p.Y511C. Although HSAN1E and ADCA-DN are proposed to be called DNMT1-complex disorders owing to their overlapping symptoms, this finding suggests a distinct genotype-phenotype correlation regarding the DNMT1 p.Y511H and p.Y511C variants.

Dislocation of stapes with footplate fracture caused by indirect trauma.

We report the first case of isolated stapedial dislocation caused by indirect head trauma, and present imaging and surgical findings in the case of a 25-year-old woman who suffered hearing loss and dizziness after head trauma caused by a traffic accident. The pure tone average was 60 dB, with an air-bone gap of 50 dB. The stapedial reflex was positive with the probe on the affected ear. Computed tomography scans revealed a longitudinal fracture of the temporal bone and a dislocated stapedial superstructure in the tympanic cavity, adhering to the tympanic membrane. During surgery, it was found that the stapes was broken at the base of the posterior crus and at the anterior one third of the footplate and that the stapedial superstructure was dislocated outward and downward, with the anterior one third of the footplate adhering to the tympanic membrane. The stapedial tendon was connected to the superstructure. Ossicular chain reconstruction was performed with success. In the present case, two mechanisms may have acted together: 1) an increase in perilymphatic pressure that caused the footplate to fracture, and 2) a distorting force that broke the posterior crus, disconnecting the incudostapedial joint, and finally dislocating the stapedial superstructure together with the anterior part of the footplate.

Existence of possible functional interaction between the saccule and the posterior semicircular canal in humans: an evaluation using VEMPs.

The purpose of this study was to determine the effects of stimulation of the vertical semicircular canals on vestibular evoked myogenic potentials (VEMPs). VEMPs were recorded in 14 subjects seated with their heads and necks tilted 120 degrees forward on the interaural axis. The head was rotated 45 degrees to the left or right from the sagittal plane; an angular acceleration around the earth's vertical axis was then provided. When the posterior semicircular canal (PSCC) of the recording side was excited, the rotation was defined as 'ipsilateral rotation', and the opposite rotation was defined as 'contralateral rotation'. The background muscle activity-corrected p13-n23 amplitude (CA) in the ipsilateral rotation was significantly smaller than CAs in the static state and the contralateral rotation. Functional interaction between the saccule and the PSCC could be detected.

Rotating computed tomographic movie for evaluating partially ossified cochlea.

OBJECTIVE: To describe our newly devised method of viewing intracochlear ossification for the purpose of minimizing bone drilling during cochlear implantation for partially ossified cochleas and to evaluate its usefulness. STUDY DESIGN: Descriptive study that compares 1) conventional computed tomographic (CT) films with the newly devised CT movie and 2) preoperative evaluation using the CT movie with the findings during surgery. SETTING: University Hospital. PATIENTS: Four cochlear implantees with partial ossification of cochlea due to meningitis. INTERVENTION: Diagnostic. MAIN OUTCOME MEASURES: Reconstruction of high-resolution CT images of the temporal bone was performed using a multiplanar reformat software. By rotating the cochlear cross plane from the round window niche in the direction of the inferior segment by 5 degrees, 72 images were obtained for 360-degree rotation, which were converted to a movie using QuickTime Pro software. The preoperative evaluation and intraoperative findings were compared. RESULTS: The advantage of CT movie over sequential CT films was facility in understanding the 3-dimensional space in the cochlea. Evaluation of the extent of the ossified region on CT movie corresponded to the intraoperative findings in all 4 patients. In 1 patient, the CT movie corrected an erroneous evaluation based on conventional CT films. However, additional drilling over the extent of ossification was necessitated in another patient because of scar tissue development. CONCLUSION: Computed tomographic movie is considered an innovative new method for preoperative evaluation of ossified cochleas and is able to reduce human errors. However, additional drilling beyond ossified part can become necessary during surgery.

Latency variation of auditory N1m responses to vocal and nonvocal sounds.

To investigate the temporal aspect of timbre processing, we recorded auditory-evoked neuromagnetic responses to periodic complex sounds, which were matched in all acoustic parameters except for two fundamental frequencies (F0s) and 12 spectral envelopes of vocal and nonvocal categories. Only for nonvocal sounds, a significant difference in N1m latency for F0 was detected in both hemispheres. A significant difference among stimuli was detected in both hemispheres for vocal and linear sounds, whereas only in the right hemisphere for instrumental sounds. Moreover, the results of paired comparison among F0s revealed that not only the vocal sounds but also some of the nonvocal sounds were F0-independent. This latency independence may be attributed to the relatively high power in the higher frequency spectrum.

Hearing levels in patients with microtia: correlation with temporal bone malformation.

OBJECTIVE: To evaluate the relationship between hearing level and temporal bone abnormalities in patients with microtia. STUDY DESIGN: Retrospective case series study between 1992 and 2004. SETTING: Academic, tertiary care referral medical center. PATIENTS: We evaluated 115 ears of 89 patients (68 males, 21 females; mean age, 11 yr; range, 5-44 yr) with microtia. MAIN OUTCOME MEASURES: Hearing level was examined in patients with microtia. Developmental abnormalities of the temporal bone were evaluated by Jahrsdoerfer's computed tomography (CT) scoring system using high-resolution CT (HRCT) scans of the temporal bone. Temporal bone malformation scores were divided into four subgroups: ossicular development, windows connected to the cochlea, aeration of the middle ear cavity, and facial nerve aberration. Patients were divided into the stenosis and atresia groups on the basis of the appearance of the external auditory canal (EAC). We also evaluated the relationships between hearing level and four subtotal scores of the HRCT findings in the stenosis and atresia groups. RESULTS: There was no relationship between hearing level and total points of HRCT scoring system or between hearing level and severity of microtia scored by Marx classification. With regard to subtotal points related to ossicles (4 points), the hearing level in ears with low scores (<2) (64.7 +/- 1.6 dB) was significantly different (P = .03) from that in ears with high scores (> or =2) (54.0 +/- 2.8 dB) in the stenosis group. In the atresia group, the hearing level was 64.3 +/- 2.2 dB in ears with low scores and 62.3 +/- 1.1 in ears with high scores (P > .5). As for subtotal points related to the windows connected to cochlea (2 points), the hearing level was 64.8 +/- 2.6 dB in ears with low scores (0) and 55.9 +/- 2.4 dB in ears with high scores (> = 1) in the stenosis group. In the atresia group, the hearing level was 67.7 +/- 2.3 dB in ears with low scores and 61.5 +/- 1.0 in ears with high scores. There was significant difference between ears with low and high scores in the stenosis group (P = .03) and atresia group (P = .009). There was no significant difference between ears with low and high scores with respect to the subtotal points related to aeration of the middle ear cavity and aberration of the facial nerve. CONCLUSION: The hearing level in microtic ears correlated with the formation of oval/round windows and ossicular development but not with the degree of middle ear aeration, facial nerve aberration, or severity of microtia. The hearing level can also serve as an indictor, such as the HRCT findings, to determine whether a subject's hearing will likely improve after reconstructive surgery.

Isolated cochlear nerve hypoplasia with various internal auditory meatus deformities in children.

OBJECTIVES: We report neuro-otological findings in isolated congenital cochlear nerve hypoplasia with various bony deformities and evaluate relationships between functional impairment and the radiologic dimensions of the internal auditory meatus (IAM). METHODS: We performed imaging and functional analyses on consecutive juvenile or adolescent patients between 2001 and 2005 with "isolated" unilateral hypoplasia of the cochlear nerve, without inner ear anomaly or other deformities. RESULTS: Among 20 patients with unilateral profound deafness who underwent imaging studies, 10 (50%) passed the inclusion criteria. In all affected ears, auditory brain stem responses were absent and the speech discrimination score was very poor (0% to 5%). Distortion product otoacoustic emissions were good in 2 ears, fair in 1 ear, and poor in 7 ears. Caloric responses were absent in 2 ears, reduced in 3 ears, and normal in 5 ears. Inferior vestibular nerve function and facial nerve function were normal in all ears. Distortion product otoacoustic emissions and caloric responses tended to be better in ears with less severe narrowing of the IAM. CONCLUSIONS: The risk of co-involvement of the inner ear and superior vestibular nerve functions is higher in the presence of a narrower bony IAM. Cochlear nerve hypoplasia is proposed as one of the most important causes of juvenile unilateral deafness because of its unexpectedly high incidence.

Successful cochlear implantation in a patient with bilateral progressive sensorineural hearing loss after traumatic subarachnoid hemorrhage and brain contusion.

OBJECTIVES: We address the proper indications for cochlear implantation for profound deafness with possible retrocochlear involvement by reporting successful implantation in a patient with traumatic subarachnoid hemorrhage and brain contusion. METHODS: We present a patient (55-year-old man) who had bilateral progressive sensorineural hearing loss after traumatic subarachnoid hemorrhage and brain contusion. Preoperative imaging and functional studies were done, as well as routine tests, to evaluate the possible performance of the cochlear implant. RESULTS: Sensorineural hearing loss developed promptly after head trauma with progressive deterioration. The cause of progressive sensorineural hearing loss remained unknown. Distortion product otoacoustic emissions demonstrated bilateral inner ear (outer hair cell) damage. Highly impaired speech discrimination despite less marked pure tone average elevation and a focal lesion in the left middle temporal gyrus suggested the possibility of coexisting retrocochlear lesions. After thorough discussion of the possible outcomes, cochlear implantation was successfully performed 25 months after the trauma. The patient became able to use a telephone. CONCLUSIONS: We advocate that profound bilateral sensorineural hearing loss caused by traumatic head injury, even with possible involvement of central auditory pathways, should not be regarded as a contraindication to cochlear implantation, as long as bilateral inner ear dysfunction is clearly demonstrated and there is no obvious evidence of central deafness.

Effect of head position on vestibular evoked myogenic potentials with toneburst stimuli.

CONCLUSION: The present study demonstrated the robustness of VEMP testing with toneburst stimuli, since it is hardly affected by head position, i.e. base or tonic excitation levels of the saccule and inferior vestibular nerve. However, the small but highly significant difference found in latency should not be neglected: the gravitational axis in the upright position may have some special effect on tonic excitation of the saccule. OBJECTIVES: To evaluate the effect of head positions on vestibular evoked myogenic potentials (VEMPs) with toneburst stimuli. MATERIALS AND METHODS: VEMPs were recorded with short tonebursts of 500 Hz in 14 normal subjects in 5 head positions (upright, nose up, ear up, nose down, and ear down). The three parameters analyzed were: 1) latency of p13, 2) latency of n23, and 3) corrected amplitude of p13-n23 (CA p13-n23). RESULTS: One-way repeated measures ANOVA showed significant effects on both p13 (p=0.0245) and n23 (p<0.0001) latencies, but not on CA p13-n23. Bonferroni's post hoc test demonstrated that there were significant differences in n23 latency between the upright position and all other head positions leaning on the bed.

Surgical treatment of medial meatal fibrosis. Report of four cases.

OBJECTIVE: We describe four cases of medial meatal fibrosis, a rare condition of the external auditory canal, in which hearing improved following surgery. METHODS: Four patients with medial meatal fibrosis underwent surgical treatment and had been followed at the University of Tokyo during the last 5 years. We examined hearing improvement and recurrence. A patient had graft-versus-host disease (GVHD) with her urethra and vagina, and two patients had methicillin resistant Staphylococcus aureus (MRSA) infection with their affected ears. RESULTS: All cases got hearing improvement without any major complications. CONCLUSIONS: Medial meatal fibrosis may be treated satisfactory with surgical interventions.

Effect of Noisy Galvanic Vestibular Stimulation on Ocular Vestibular-Evoked Myogenic Potentials to Bone-Conducted Vibration.

OBJECTIVE: Galvanic vestibular stimulation (GVS) delivered as zero-mean current noise (noisy GVS) has been shown to improve static and dynamic postural stability probably by enhancing vestibular information. The purpose of this study was to examine the effect of an imperceptible level noisy GVS on ocular vestibular-evoked myogenic potentials (oVEMPs) in response to bone-conducted vibration (BCV). MATERIALS AND METHODS: oVEMPs to BCV were measured during the application of white noise GVS with an amplitude ranging from 0 to 300 µA [in root mean square (RMS)] in 20 healthy subjects. Artifacts in the oVEMPs caused by GVS were reduced by inverting the waveforms of noisy GVS in the later half of the stimulus from the one in the early half. We examined the amplitudes of N1 and N1-P1 and their latencies. RESULTS: Noisy GVS significantly increased the N1 and N1-P1 amplitudes (p < 0.05) whereas it had no significant effects on N1 or P1 latencies (p > 0.05). Noisy GVS had facilitatory effects in 79% of ears. The amplitude of the optimal stimulus was 127 ± 14 µA, and it increased the N1 and N1-P1 amplitude by 75.9 ± 15% and 47.7 ± 9.1%, respectively, as compared with 0 µA session (p < 0.05). CONCLUSION: Noisy GVS can increase the amplitude of oVEMPs to BCV in healthy subjects probably via stochastic resonance. The results of the present study suggest that noisy GVS may improve static and dynamic postural stability by enhancing the function of the vestibular afferents.

Prediction of Intraoperative CSF Gusher and Postoperative Facial Nerve Stimulation in Patients With Cochleovestibular Malformations Undergoing Cochlear Implantation Surgery.

OBJECTIVE: To determine parameters in computed tomography (CT) of the temporal bone that would be useful for prediction of cerebrospinal fluid (CSF) gusher during cochlear implantation (CI) surgery and postoperative facial nerve stimulation (FNS) in patients with inner ear malformations. STUDY DESIGN: Retrospective study. SETTING: Tertiary referral center. PATIENTS: Three hundred seventy-five cases who had undergone CI surgery including 54 inner ear malformation cases were analyzed. MAIN OUTCOME MEASURES: The diameters of the cochlea modiolar base and porus of the internal auditory canal (IAC), length of IAC, diameter of the vestibular aqueduct (VA) at the operculum, and presence or absence of the modiolus of the cochlea were evaluated by using CT. RESULTS: CSF gusher occurred in 12 (22%) cases, in whom the diameters of the cochlea modiolar base (2.7 ±â€Š0.6 mm, p < 0.01) and widths of VA (1.5 ±â€Š1.0 mm, p < 0.05) were significantly greater compared with those without gusher. The modiolus was significantly less formed (8%) in cases with gusher compared with those without gusher (p < 0.01). FNS occurred in 10 (19%) cases, and the widths of VA and lengths of IAC were significantly shorter in these cases compared with those without FNS (p < 0.05). CONCLUSION: The absence of the modiolus, larger cochlea modiolar base, and wider VA in CT images were important predictors of CSF gusher during CI surgery. The width of VA was also an important factor in predicting FNS.

Free anterolateral thigh full-thickness skin flap with vascularized lateral femoral cutaneous nerve for the reconstruction of facial nerve and external auditory canal after the resection of facial nerve schwannoma.

The complex reconstruction of nerves and soft tissue in the head and neck region is still challenging, especially in cases requiring external auditory canal reconstruction with facial nerve reconstruction. We report a case of left facial schwannoma extending into the external auditory canal beyond the tympanic membrane with facial paralysis in which the reconstruction of both the facial nerve and external auditory canal was successfully performed using an anterolateral thigh flap as a super-thin full-thickness skin flap, including vascularized lateral femoral cutaneous nerve. Resection of 20 mm × 46 mm facial schwannoma, including the skin of the external auditory canal, tympanic membrane, incus and malleus, was performed. The 8-cm nerve gap was repaired using a vascularized lateral femoral cutaneous nerve included in the anterolateral thigh flap. An 8 cm × 2 cm super-thin, free anterolateral thigh flap was then rolled up as a sac (diameter of 2 cm, height of 2 cm) and inset to the external auditory canal defect. The postoperative course was uneventful, and the flap survived completely. One year and nine months after the surgery, the patient's facial movement has improved to the pre-surgery level.

A magnetoencephalographic study of Japanese vowel processing.

Magnetic brain responses were recorded to clarify the cortical representation of vowel processing in Japanese. We investigated the peak latencies and equivalent current dipoles of the auditory N1m responses to the Japanese vowels [a], [i], [o], and [u]. In intraindividual analyses for a single participant, well-replicated results for the dipole parameters supported the existence of phoneme-specific cortical maps for vowels. In the interindividual analyses for the eight participants, [a] and [i] elicited significantly earlier N1m responses than [u], and the dipole for [i] was more posteriorly oriented than [a] in the left hemisphere. The results of the current study suggest left hemispheric predominance in vowel processing and that factors associated with a different language system may modify the cortical map.

Bone-conducted auditory brainstem-evoked responses and skull vibratory velocity measurement in rats at frequencies of 0.5-30 kHz with a new giant magnetostrictive bone conduction transducer.

CONCLUSIONS: A new giant magnetostrictive bone conduction transducer (GMT) measuring 8 mm (length) by 2 mm (diameter) is capable of outputting sounds over a wider range of frequencies than conventional electromagnetic transducers (EMTs). The GMT can vibrate the rat skull about 3-100 times faster than the EMT, especially above 2 kHz. OBJECTIVES: Since the GMT can generate high sound quality and output sounds above 10 kHz, we investigated the width of the frequency response of the GMT and evaluated its mechanical performance. MATERIALS AND METHODS: We chose Wistar rats to estimate the GMT performance by measuring the bone-conducted ABR and the skull vibratory velocity because their hearing frequency range extends from 0.15 kHz to 67 kHz. We also measured the bone-conducted auditory brainstem responses (ABRs) and the skull vibratory velocity of rats with the EMT. Skull vibratory velocity was measured with a laser Doppler vibrometer (LDV). RESULTS: The skull vibratory velocity at the ABR threshold obtained with each transducer was within the -35 to -50 dB range (0 dB re 1 mm/s). When 1 Vpp was applied to each transducer, the GMT had a higher velocity at frequencies of 2-30 kHz, and the EMT at frequencies of 0.5-1 kHz.

Development of auditory skills after cochlear implantation in children with inner ear malformations.

CONCLUSIONS: CI improves hearing thresholds and auditory skills in children with most types of inner ear malformations. However, the development of sound detection skills is not as good as it is in children without inner ear malformations. OBJECTIVES: To investigate the influence of inner ear malformations on development of auditory skills after cochlear implantation (CI). METHODS: Records of 20 children with inner ear malformations who underwent cochlear implantation before 4 years of age and followed up for more than 2 years were retrospectively reviewed. Hearing thresholds, the Meaningful Auditory Integration Scale (MAIS), and Meaningful Use of Speech Scale (MUSS) scores before and after CI were analyzed and compared with 20 age-matched deaf children who underwent CI. RESULTS: The children with inner ear malformations showed significant improvements in hearing thresholds and the MAIS and MUSS scores 1 year after CI (p < 0.01). However, their development of the MAIS scores was significantly delayed compared to children without inner ear malformations (p < 0.05), while there was no significant difference in development of the MUSS scores between them. Significant improvements in hearing thresholds and the MAIS and MUSS scores were observed in cochlear hypoplasia and incomplete partition (p < 0.05).

The Hearing Outcomes of Cochlear Implantation in Waardenburg Syndrome.

Objectives. This study aimed to determine the feasibility of cochlear implantation for sensorineural hearing loss in patients with Waardenburg syndrome. Method. A retrospective chart review was performed on patients who underwent cochlear implantation at the University of Tokyo Hospital. Clinical classification, genetic mutation, clinical course, preoperative hearing threshold, high-resolution computed tomography of the temporal bone, and postoperative hearing outcome were assessed. Result. Five children with Waardenburg syndrome underwent cochlear implantation. The average age at implantation was 2 years 11 months (ranging from 1 year 9 months to 6 years 3 months). Four patients had congenital profound hearing loss and one patient had progressive hearing loss. Two patients had an inner ear malformation of cochlear incomplete partition type 2. No surgical complication or difficulty was seen in any patient. All patients showed good hearing outcome postoperatively. Conclusion. Cochlear implantation could be a good treatment option for Waardenburg syndrome.