Acoustic Reflexes in Aural Atresia Patients: Evidence of an Intact Efferent System?

OBJECTIVE: To record crossed acoustic reflex thresholds (xART's) postoperatively from patients after surgical repair of unilateral congenital aural atresia (CAA). To seek explanations for when xARTs can and cannot be recorded. We hope to understand the implications for this central auditory reflex despite early afferent deprivation. METHODS: Patients who underwent surgery to correct unilateral CAA at a tertiary academic medical were prospectively enrolled to evaluate for the presence of xART. Preoperative ARTs in the normal (non-atretic) ear, and postoperative ipsilateral ARTs (stimulus in the normal ear) and contralateral ARTs (stimulus in the newly reconstructed atretic ear; record in the normal ear) were measured at 500, 1000, and 2000 Hz. RESULTS: Four of 11 patients with normal ipsilateral reflex thresholds preoperatively demonstrated crossed acoustic reflexes postoperatively (stimulus in reconstructed ear; record from normal ear). Four other patients demonstrated normal ipsilateral thresholds preoperatively but did not have crossed reflexes postoperatively. No reflexes (pre- or postoperatively) could be recorded in 3 patients. Crossed reflex threshold is significantly correlated with the postoperative audiometric threshold. There was no correlation between ipsilateral and contralateral reflex thresholds. CONCLUSION: Crossed acoustic reflexes can be recorded from some but not all postoperative atresia patients, and the thresholds for those reflexes correlate with the postoperative pure tone threshold. The presence of acoustic reflexes implies an intact CN VIII-to-opposite CN VII central reflex arc despite early unilateral sound deprivation.

The brain of the African wild dog. III. The auditory system.

The large external pinnae and extensive vocal repertoire of the African wild dog (Lycaon pictus) has led to the assumption that the auditory system of this unique canid may be specialized. Here, using cytoarchitecture, myeloarchitecture, and a range of immunohistochemical stains, we describe the systems-level anatomy of the auditory system of the African wild dog. We observed the cochlear nuclear complex, superior olivary nuclear complex, lateral lemniscus, inferior colliculus, medial geniculate body, and auditory cortex all being in their expected locations, and exhibiting the standard subdivisions of this system. While located in the ectosylvian gyri, the auditory cortex includes several areas, resembling the parcellation observed in cats and ferrets, although not all of the auditory areas known from these species could be identified in the African wild dog. These observations suggest that, broadly speaking, the systems-level anatomy of the auditory system, and by extension the processing of auditory information, within the brain of the African wild dog closely resembles that observed in other carnivores. Our findings indicate that it is likely that the extraction of the semantic content of the vocalizations of African wild dogs, and the behaviors generated, occurs beyond the classically defined auditory system, in limbic or association neocortical regions involved in cognitive functions. Thus, to obtain a deeper understanding of how auditory stimuli are processed, and how communication is achieved, in the African wild dog compared to other canids, cortical regions beyond the primary sensory areas will need to be examined in detail.

Neural Encoding of Amplitude Modulations in the Human Efferent System.

Most natural sounds, including speech, exhibit temporal amplitude fluctuations. This information is encoded as amplitude modulations (AM)-essential for auditory and speech perception. The neural representation of AM has been studied at various stages of the ascending auditory system from the auditory nerve to the cortex. In contrast, research on neural coding of AM in the efferent pathway has been extremely limited. The objective of this study was to investigate the encoding of AM signals in the medial olivocochlear system by measuring the modulation transfer functions of the efferent response in humans. A secondary goal was to replicate the controversial findings from the literature that efferent stimulation produces larger effects for the AM elicitor with 100 Hz modulation frequency in comparison with the unmodulated elicitor. The efferent response was quantified by measuring changes in stimulus-frequency otoacoustic emission magnitude due to various modulated and unmodulated elicitors. Unmodulated, broadband noise elicitors yielded either slightly larger or similar efferent responses relative to modulated elicitors depending on the modulation frequency. Efferent responses to the unmodulated and modulated elicitors with 100 Hz modulation frequency were not significantly different. The efferent system encoding of AM sounds-modulation transfer functions-can be modeled with a first-order Butterworth low-pass filter with different cutoff frequencies for ipsilateral and contralateral elicitors. The ipsilateral efferent pathway showed a greater sensitivity to AM information comparted to the contralateral pathway. Efferent modulation transfer functions suggest that the ability of the system to follow AM decreases with increasing modulation frequency and that efferents may not be fully operating on the envelope of the speech.

A re-evaluation of the basicranial soft tissues and pneumaticity of the therizinosaurian Nothronychus mckinleyi (Theropoda; Maniraptora).

The soft-tissue reconstruction and associated osteology of the North American therizinosaurian Nothronychus mckinleyi is updated. The cranial nerve topology is revised, bringing it more in line with coelurosaurs. The trunk of the trigeminal nerve is very short, with an incompletely intracranial trigeminal ganglion, an ophthalmic branch diverging anteriorly first, with later divergences of the maxillomandibular branches, following typical pathways. The facial nerve has been re-evaluated, resulting in a very typical configuration with an extracranial geniculate ganglion. The single foramen leading to the cochlea probably transmitted the vestibulocochlear nerve, along with some fibers of the facial. This configuration is reduced from the more standard three foramina (vestibular, cochlear, and facial) and may be apomorphic for therizinosaurs. Some alteration is proposed for the dorsiflexive musculature. The insertion point for m. transversospinalis capitis is partially changed to extend onto the parietal, along with a proposed functional difference in the moment arm. The expansion of the basicranial pneumatic system is limited to the paratympanic system, enhancing low frequency sound sensitivity. There is little expansion of the median pharyngeal and subcondylar sinuses. Ossification of the surrounding epithelium may provide some information on the embryology of the theropod skull. It may be associated with a reduced stress field, or the general similarity of the basicranium with anterior cervical vertebrae may reflect activation of a cervical vertebral (Hox) gene regulating ossification of the pneumatic sinuses. This might be a local, selectively neutral, fixed gene in the basicranium reflecting embryological regulation of cervical vertebrae development.

ECAP growth function to increasing pulse amplitude or pulse duration demonstrates large inter-animal variability that is reflected in auditory cortex of the guinea pig.

Despite remarkable advances made to ameliorate how cochlear implants process the acoustic environment, many improvements can still be made. One of most fundamental questions concerns a strategy to simulate an increase in sound intensity. Psychoacoustic studies indicated that acting on either the current, or the duration of the stimulating pulses leads to perception of changes in how loud the sound is. The present study compared the growth function of electrically evoked Compound Action Potentials (eCAP) of the 8th nerve using these two strategies to increase electrical charges (and potentially to increase the sound intensity). Both with chronically (experiment 1) or acutely (experiment 2) implanted guinea pigs, only a few differences were observed between the mean eCAP amplitude growth functions obtained with the two strategies. However, both in chronic and acute experiments, many animals showed larger increases of eCAP amplitude with current increase, whereas some animals showed larger of eCAP amplitude with duration increase, and other animals show no difference between either approaches. This indicates that the parameters allowing the largest increase in eCAP amplitude considerably differ between subjects. In addition, there was a significant correlation between the strength of neuronal firing rate in auditory cortex and the effect of these two strategies on the eCAP amplitude. This suggests that pre-selecting only one strategy for recruiting auditory nerve fibers in a given subject might not be appropriate for all human subjects.

MicroRNA-194 Regulates the Development and Differentiation of Sensory Patches and Statoacoustic Ganglion of Inner Ear by Fgf4.

BACKGROUND MicroRNA 194 is involved in the differentiation of various types of cells, such as adipose derived stem cells, human embryonic stem cells, and bone marrow mesenchymal stem cells. Previously, we found that miR-194 was highly expressed in the inner ear sensory patch and neurons in mice embryos. However, the role of miR-194 in the development of the inner ear and its underlying mechanism have not been elucidated yet. MATERIAL AND METHODS The expression level of miR-194 has been altered by using antisense morpholino oligonucleotides (MO) and synthesized miRNAs in zebrafish. RESULTS We found that miR-194 was vastly expressed in the inner ear and central nervous system (CNS) in zebrafish. Loss of function of miR-194 could strongly affected the development of zebrafish embryos, including delayed embryonic development, edema of the pericardium, small head, axial deviation, delayed development of inner ear, closer location of two otoliths, delayed fusion of the semicircular canals, and abnormal otolith number in some cases. In addition, the behavior of zebrafish was also adversely affected with impaired balance and biased swimming route. Misexpression of miR-194 could strongly affected the development and differentiation of spiral ganglion neuron (SGN) in inner ear through Fgf4 in vitro. Similar results have also been observed that the overexpression and knockdown of miR-194 strongly disturbed the development and differentiation of the sensory patches and Statoacoustic ganglion (SAG) through Fgf4 in zebrafish in vivo. Our results indicated that miR-194 may regulate the development and differentiation of sensory patches and SAG through Fgf4. CONCLUSIONS Our data revealed a vital role of miR-194 in regulating the development and differentiation of the inner ear.

Congress of Neurological Surgeons Systematic Review and Evidence-Based Guidelines on Intraoperative Cranial Nerve Monitoring in Vestibular Schwannoma Surgery.

Question 1: Does intraoperative facial nerve monitoring during vestibular schwannoma surgery lead to better long-term facial nerve function? Target Population: This recommendation applies to adult patients undergoing vestibular schwannoma surgery regardless of tumor characteristics. Recommendation: Level 3: It is recommended that intraoperative facial nerve monitoring be routinely utilized during vestibular schwannoma surgery to improve long-term facial nerve function. Question 2: Can intraoperative facial nerve monitoring be used to accurately predict favorable long-term facial nerve function after vestibular schwannoma surgery? Target Population: This recommendation applies to adult patients undergoing vestibular schwannoma surgery. Recommendation: Level 3: Intraoperative facial nerve can be used to accurately predict favorable long-term facial nerve function after vestibular schwannoma surgery. Specifically, the presence of favorable testing reliably portends a good long-term facial nerve outcome. However, the absence of favorable testing in the setting of an anatomically intact facial nerve does not reliably predict poor long-term function and therefore cannot be used to direct decision-making regarding the need for early reinnervation procedures. Question 3: Does an anatomically intact facial nerve with poor electromyogram (EMG) electrical responses during intraoperative testing reliably predict poor long-term facial nerve function? Target Population: This recommendation applies to adult patients undergoing vestibular schwannoma surgery. Recommendation: Level 3: Poor intraoperative EMG electrical response of the facial nerve should not be used as a reliable predictor of poor long-term facial nerve function. Question 4: Should intraoperative eighth cranial nerve monitoring be used during vestibular schwannoma surgery? Target Population: This recommendation applies to adult patients undergoing vestibular schwannoma surgery with measurable preoperative hearing levels and tumors smaller than 1.5 cm. Recommendation: Level 3: Intraoperative eighth cranial nerve monitoring should be used during vestibular schwannoma surgery when hearing preservation is attempted. Question 5: Is direct monitoring of the eighth cranial nerve superior to the use of far-field auditory brain stem responses? Target Population: This recommendation applies to adult patients undergoing vestibular schwannoma surgery with measurable preoperative hearing levels and tumors smaller than 1.5 cm. Recommendation: Level 3: There is insufficient evidence to make a definitive recommendation. The full guideline can be found at: https://www.cns.org/guidelines/guidelines-manage-ment-patients-vestibular-schwannoma/chapter_4.

Differentiating Middle Ear and Medial Olivocochlear Effects on Transient-Evoked Otoacoustic Emissions.

The response of the inner ear is modulated by the middle ear muscle (MEM) and olivocochlear (OC) efferent systems. Both systems can be activated reflexively by acoustic stimuli delivered to one or both ears. The acoustic middle ear muscle reflex (MEMR) controls the transmission of acoustic signals through the middle ear, while reflex activation of the medial component of the olivocochlear system (the MOCR) modulates cochlear mechanics. The relative prominence of the two efferent systems varies widely between species. Measuring the effect of either of these systems can be confounded by simultaneously activating the other. We describe a simple, sensitive online method that can identify the effects both systems have on otoacoustic emissions (OAEs) evoked by transient stimuli such as clicks or tone pips (TEOAEs). The method detects directly in the time domain the changes in the stimulus and/or emission pressures caused by contralateral noise. Measurements in human participants are consistent with other reports that the threshold for MOCR activation is consistently lower than for MEMR. The method appears to control for drift and subject-generated noise well enough to avoid the need for post hoc processing, making it promising for application in animal experiments (even if awake) and in the hearing clinic.

Identifying the Origin of Effects of Contralateral Noise on Transient Evoked Otoacoustic Emissions in Unanesthetized Mice.

Descending neural pathways in the mammalian auditory system are known to modulate the function of the peripheral auditory system. These pathways include the medial olivocochlear (MOC) efferent innervation to outer hair cells (OHCs) and the acoustic reflex pathways mediating middle ear muscle (MEM) contractions. Based on measurements in humans (Marks and Siegel, companion paper), we applied a sensitive method to attempt to differentiate MEM and MOC reflexes using contralateral acoustic stimulation in mice under different levels of anesthesia. Separation of these effects is based on the knowledge that OHC-generated transient evoked otoacoustic emissions (TEOAE) are delayed relative to the stimulus, and that the MOC reflex affects the emission through its innervation of OHC. In contrast, the MEM-mediated changes in middle ear reflectance alter both the stimulus (with a short delay) and the emission. Using this approach, time averages to transient stimuli were evaluated to determine if thresholds for a contralateral effect on the delayed emission, indicating potential MOC activation, could be observed in the absence of a change in the stimulus pressure. This outcome was not observed in the majority of cases. There were also no statistically significant differences between MEM and putative MOC thresholds, and variability was high for both thresholds regardless of anesthesia level. Since the two reflex pathways could not be differentiated on the basis of activation thresholds, it was concluded that the MEM reflex dominates changes in TEOAEs induced by contralateral noise. This result complicates the identification of purely MOC-induced changes on OAEs in mice unless the MEM reflex is inactivated surgically or pharmacologically.

Effect of Contralateral Medial Olivocochlear Feedback on Perceptual Estimates of Cochlear Gain and Compression.

The active cochlear mechanism amplifies responses to low-intensity sounds, compresses the range of input sound intensities to a smaller output range, and increases cochlear frequency selectivity. The gain of the active mechanism can be modulated by the medial olivocochlear (MOC) efferent system, creating the possibility of top-down control at the earliest level of auditory processing. In humans, MOC function has mostly been measured by the suppression of otoacoustic emissions (OAEs), typically as a result of MOC activation by a contralateral elicitor sound. The exact relationship between OAE suppression and cochlear gain reduction, however, remains unclear. Here, we measured the effect of a contralateral MOC elicitor on perceptual estimates of cochlear gain and compression, obtained using the established temporal masking curve (TMC) method. The measurements were taken at a signal frequency of 2 kHz and compared with measurements of click-evoked OAE suppression. The elicitor was a broadband noise, set to a sound pressure level of 54 dB to avoid triggering the middle ear muscle reflex. Despite its low level, the elicitor had a significant effect on the TMCs, consistent with a reduction in cochlear gain. The amount of gain reduction was estimated as 4.4 dB on average, corresponding to around 18 % of the without-elicitor gain. As a result, the compression exponent increased from 0.18 to 0.27.

Sound coding in the auditory nerve of gerbils.

Gerbils possess a very specialized cochlea in which the low-frequency inner hair cells (IHCs) are contacted by auditory nerve fibers (ANFs) having a high spontaneous rate (SR), whereas high frequency IHCs are innervated by ANFs with a greater SR-based diversity. This specificity makes this animal a unique model to investigate, in the same cochlea, the functional role of different pools of ANFs. The distribution of the characteristic frequencies of fibers shows a clear bimodal shape (with a first mode around 1.5 kHz and a second around 12 kHz) and a notch in the histogram near 3.5 kHz. Whereas the mean thresholds did not significantly differ in the two frequency regions, the shape of the rate-intensity functions does vary significantly with the fiber characteristic frequency. Above 3.5 kHz, the sound-driven rate is greater and the slope of the rate-intensity function is steeper. Interestingly, high-SR fibers show a very good synchronized onset response in quiet (small first-spike latency jitter) but a weak response under noisy conditions. The low-SR fibers exhibit the opposite behavior, with poor onset synchronization in quiet but a robust response in noise. Finally, the greater vulnerability of low-SR fibers to various injuries including noise- and age-related hearing loss is discussed with regard to patients with poor speech intelligibility in noisy environments. Together, these results emphasize the need to perform relevant clinical tests to probe the distribution of ANFs in humans, and develop appropriate techniques of rehabilitation. This article is part of a Special Issue entitled .

Mentalis muscle related reflexes.

The mentalis muscle (MM) arises from the incisive fossa of the mandible, raises and protrudes the lower lip. Here, we aim to characterize responses obtained from MM by supraorbital and median electrical as well as auditory stimuli in a group of 16 healthy volunteers who did not have clinical palmomental reflex. Reflex activities were recorded from the MM and orbicularis oculi (O.oc) after supraorbital and median electrical as well as auditory stimuli. Response rates over MM were consistent after each stimulus, however, mean latencies of MM response were longer than O.oc responses by all stimulation modalities. Shapes and amplitudes of responses from O.oc and MM were similar. Based on our findings, we may say that MM motoneurons have connections with trigeminal, vestibulocochlear and lemniscal pathways similar to other facial muscles and electrophysiological recording of MM responses after electrical and auditory stimulation is possible in healthy subjects.

Diffusion tensor tractography of normal facial and vestibulocochlear nerves.

PURPOSE: Diffusion tensor tractography (DTT) is not adequately reliable for prediction of facial and vestibulocochlear (VII-VIII) nerve locations, especially relative to a vestibular schwannoma (VS). Furthermore, it is often not possible to visualize normal VII-VIII nerves by DTT (visualization rates were 12.5-63.6%). Therefore, DTT post-processing was optimized for normal VII-VIII nerve visualization with and without manual noise elimination. METHODS: DTT examinations of ten patients were evaluated to assess the improvement in performance by modifying seed region of interest (ROI) and fractional anisotropy (FA) threshold. Seed ROI was placed at the porus of the internal auditory meatus, and FA threshold values were either fixed or variable for each patient. DTT visualization of cranial nerves VII-VIII was evaluated and the noise effect was measured. RESULTS: Cranial nerves VII-VIII were visualized in 90% of patients without using manual noise elimination by modifying the seed ROI and FA threshold. The visualization rate with FA threshold of the upper limit in each patient (100%) was significantly higher than that with FA threshold of 0.1 (75%) (p = 0.02). The incidence rate of noise with FA threshold of the upper limit (10%) was not significantly different than the FA threshold of 0.1 (20%) (p = 0.66). CONCLUSION: Seed ROI modification and FA thresholding can improve the visualization of cranial nerve VII-VIII locations in DTT. This technique is promising for its potential to determine the relationship of cranial nerves VII-VIII to VS.

Reducing Current Spread by Use of a Novel Pulse Shape for Electrical Stimulation of the Auditory Nerve.

Improving the electrode-neuron interface to reduce current spread between individual electrodes has been identified as one of the main objectives in the search for future improvements in cochlear-implant performance. Here, we address this problem by presenting a novel stimulation strategy that takes account of the biophysical properties of the auditory neurons (spiral ganglion neurons, SGNs) stimulated in electrical hearing. This new strategy employs a ramped pulse shape, where the maximum amplitude is achieved through a linear slope in the injected current. We present the theoretical framework that supports this new strategy and that suggests it will improve the modulation of SGNs' activity by exploiting their sensitivity to the rising slope of current pulses. The theoretical consequence of this sensitivity to the slope is a reduction in the spread of excitation within the cochlea and, consequently, an increase in the neural dynamic range. To explore the impact of the novel stimulation method on neural activity, we performed in vitro recordings of SGNs in culture. We show that the stimulus efficacy required to evoke action potentials in SGNs falls as the stimulus slope decreases. This work lays the foundation for a novel, and more biomimetic, stimulation strategy with considerable potential for implementation in cochlear-implant technology.

Durability of hearing preservation after microsurgical treatment of vestibular schwannoma using the middle cranial fossa approach.

OBJECT: The middle cranial fossa (MCF) approach is a microsurgical technique described as a primary option in the treatment of small, intracanalicular schwannomas involving the eighth cranial nerve. Excellent rates of complete tumor resection, hearing preservation, preservation of facial nerve function, and low complication rates have been reproduced using this technique. However, the durability of hearing preservation attained using the various treatment options has not been adequately assessed. The purpose of this study was to evaluate the durability of long-term hearing preservation in patients with vestibular schwannoma (VS) treated via the MCF approach. The authors hypothesize that hearing preservation in these patients will prove to be durable years after treatment in a high percentage of cases. METHODS: Retrospective medical chart review was performed in 103 consecutive patients undergoing resection of VS via a modified MCF approach between 1999 and 2008. Patients in whom surgical goals were gross-total resection and hearing preservation were included. Preoperative and postoperative hearing assessment was performed using standard audiometric testing, and classified according to American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) guidelines as a primary outcome measure. Outcomes and neurological complications initially, and at 1, 3, and 5 years following operation were analyzed. RESULTS: Initial hearing preservation rates were in keeping with the best previously published results. At initial postoperative audiometric follow-up, of the patients presenting with Class A hearing, 67% remained Class A, 17% were Class B, 1% were Class C, and 15% were Class D. Of patients presenting with Class B hearing, 24% were Class A, 53% remained Class B, 6% were Class C, and 18% were Class D. Of patients presenting with Class C hearing, 100% remained Class C. To assess the durability of hearing preservation in our patients, the authors evaluated hearing function at regular intervals after the initial postoperative audiometric follow-up. Audiometric data were available for 56 patients at 5-year follow-up. Of the 20 patients with Class A hearing at initial postoperative follow-up with 5-year follow-up, 13 (65%) remained Class A, 6 (30%) were Class B, and 1 (5%) was Class C. Of the 12 patients with Class B hearing at initial postoperative follow-up with 5-year follow-up, 4 (33%) were Class A, 4 (33%) remained Class B, and 4 (33%) were Class C. Of the 3 patients with Class C hearing at initial postoperative follow-up with 5-year follow-up, all 3 (100%) remained Class C. CONCLUSIONS: A majority of patients with preserved hearing following the MCF approach for treatment of VS experience durability of their preserved hearing at 5-year follow-up. The initial AAO-HNS classification was preserved in 13 (65%) of the 20 patients who had Class A hearing at 5 years, and in 8 (67%) of the 12 who had Class B hearing at 5 years. Overall, a decline in AAO-HNS classification was noted in 15% of patients with preserved Class A hearing, and in 33% of those with preserved Class B hearing. Facial nerve function was preserved in 91% of cases. Superior hearing preservation as well as good outcomes in facial nerve function and few serious complications can be accomplished using the MCF approach for resection of small VSs.

Vestibular-mediated synaptic inputs and pathways to sympathetic preganglionic neurons in the neonatal mouse.

To assess when vestibulosympathetic projections become functional postnatally, and to establish a preparation in which vestibulosympathetic circuitry can be characterized more precisely, we used an optical approach to record VIIIth nerve-evoked synaptic inputs to thoracic sympathetic preganglionic neurons (SPNs) in newborn mice. Stimulation of the VIIIth nerve was performed in an isolated brainstem-spinal cord preparation after retrogradely labelling with the fluorescent calcium indicator Calcium Green 1-conjugated dextran amine, the SPNs and the somatic motoneurons (MNs) in the thoracic (T) segments T2, 4, 6, 8, 10 and 12. Synaptically mediated calcium responses could be visualized and recorded in individual SPNs and MNs, and analysed with respect to latency, temporal pattern, magnitude and synaptic pharmacology. VIIIth nerve stimulation evoked responses in all SPNs and MNs investigated. The SPN responses had onset latencies from 90 to 200 ms, compared with much shorter latencies in MNs, and were completely abolished by mephenesin, a drug that preferentially reduces polysynaptic over monosynaptic transmission. Bicuculline and picrotoxin, but not strychnine, increased the magnitudes of the SPN responses without changing the onset latencies, suggesting a convergence of concomitant excitatory and inhibitory synaptic inputs. Lesions strategically placed to test the involvement of direct vestibulospinal pathways versus indirect pathways within the brainstem showed that vestibulosympathetic inputs in the neonate are mediated predominantly, if not exclusively, by the latter. Thus, already at birth, synaptic connections in the vestibulosympathetic reflex are functional and require the involvement of the ventrolateral medulla as in adult mammals.

In vivo characterization of the vestibulo-cochlear nerve motion by MRI.

The motion of the vestibulo-cochlear nerve (VCN) was quantified at the level of the cerebello-pontine angle in 28 healthy volunteers enrolled in a prospective study performed on a 3T MRI scanner. A phase contrast MRI (PCMRI) sequence was used. The VCN was divided into a cisternal part and a meatic part, both of which were measured for motion in the cranio-caudal (CC) and antero-posterior (AP) directions. Motion was cardiac-cycle-dependent in these two directions. The meatic VCN motion was delayed compared to the cisternal VCN motion. In the CC direction, the mean amplitude of the cisternal VCN motion was twice larger than the mean amplitude of the meatic VCN motion (0.37+/-0.14 mm versus 0.17+/-0.08 mm). In the AP direction, the mean amplitude of the cisternal VCN was 0.19+/-0.08 mm versus 0.16+/-0.14 mm for the meatic VCN. We used an "oscillating string" to explain the VCN motion. Reproducibility tests have shown small variations in measurements of the CC motion. PCMRI can be used to assess the VCN motion at the level of the cerebello-pontine angle.

Neurophysiologic intraoperative monitoring of the vestibulocochlear nerve.

Neurosurgical procedures involving the skull base and structures within can pose a significant risk of damage to the brain stem and cranial nerves. This can have life-threatening consequences and/or result in devastating neurologic deficits. Over the past decade, intraoperative neurophysiology has significantly evolved and currently offers a great tool for live monitoring of the integrity of nervous structures. Thus, dysfunction can be identified early and prompt modification of the surgical management or operating conditions, leads to avoidance of permanent structural damage.Along these lines, the vestibulocochlear nerve (CN VIII) and, to a greater extent, the auditory pathways as they pass through the brain stem are especially at risk during cerebelopontine angle (CPA), posterior/middle fossa, or brain stem surgery. CN VIII can be damaged by several mechanisms, from vascular compromise to mechanical injury by stretch, compression, dissection, and heat injury. Additionally, cochlea itself can be significantly damaged during temporal bone drilling, by noise, mechanical destruction, or infarction, and because of rupture, occlusion, or vasospasm of the internal auditory artery.CN VIII monitoring can be successfully achieved by live recording of the function of one of its parts, the cochlear or auditory nerve (AN), using the brain stem auditory evoked potentials (BAEPs), electrocochleography (ECochG), and compound nerve action potentials (CNAPs) of the cochlear nerve.This is a review of these techniques, their principle, applications, methodology, interpretation of the evoked responses, and their change from baseline, within the context of surgical and anesthesia environments, and finally the appropriate management of these changes.

[Linear accelerator radiosurgery for the treatment of vestibular schwannoma]. / Radiocirugia con acelerador lineal en el tratamiento del schwannoma vestibular.

INTRODUCTION AND AIM: Radiosurgery is among the treatment options for patients with vestibular schwannoma. We present the experience in our institution in the treatment of this disease with this technique. PATIENTS AND METHODS: A retrospective study was made including 20 patients (11 women and 9 men; median age: 55.15 years-old) with vestibular schwannoma who received linear accelerator radiosurgery treatment since April 2005 until December 2008. Follow-up period was between 12 and 42 months, considering clinical examination of cranial nerves VII (House-Brackmann scale) and VIII (Gardner-Robertson scale) as well as radiological findings (considering tumor volume). For statistical analysis, the Fisher's exact test and logistic regression test were used. RESULTS: Certain worsening of hearing function was present in 25% of the patients. Five patients had large tumors at the moment of the treatment (equal or larger than 3.5 cm3), from which four deteriorated from headache, unsteady gait, dizziness/vertigo, facial numbness and tinnitus, with statistical significance (p < 0.05). From the first year of treatment on, there was a tumor volume decrease tendency, with no tumor growth in the medium/long term follow-up, achieving a local control rate of 100%. CONCLUSIONS: Radiosurgery has become an alternative in the treatment of patients with vestibular schwannoma of appropriate size, with high safety level, using low radiation doses, low rate of complications and good tumor control rate in the medium term follow-up.

Segmental patterns of vestibular-mediated synaptic inputs to axial and limb motoneurons in the neonatal mouse assessed by optical recording.

Proper control of movement and posture occurs partly via descending projections from the vestibular nuclei to spinal motor circuits. Days before birth in rodents, vestibulospinal neurons develop axonal projections that extend to the spinal cord. How functional these projections are just after birth is unknown. Our goal was to assess the overall functional organization of vestibulospinal inputs to spinal motoneurons in a brainstem-spinal cord preparation of the neonatal mouse (postnatal day (P) 0-5). Using calcium imaging, we recorded responses evoked by electrical stimulation of the VIIIth nerve, in many motoneurons simultaneously throughout the spinal cord (C2, C6, T7, L2 and L5 segments), in the medial and lateral motor columns. Selective lesions in the brainstem and/or spinal cord distinguished which tracts contributed to the responses: those in the cervical cord originated primarily from the medial vestibulospinal tracts but with a substantial contribution from the lateral vestibulospinal tract; those in the thoracolumbar cord originated exclusively from the lateral vestibulospinal tract. In the thoracolumbar but not the cervical cord, excitatory commissural connections mediated vestibular responses in contralateral motoneurons. Pharmacological blockade of GABA(A) receptors showed that responses involved a convergence of excitatory and inhibitory inputs which in combination produced temporal response patterns specific for different segmental levels. Our results show that by birth vestibulospinal projections in rodents have already established functional synapses and are organized to differentially regulate activity in neck and limb motoneurons in a tract- and segment-specific pattern similar to that in adult mammals. Thus, this particular set of descending projections develops several key features of connectivity appropriately at prenatal stages. We also present novel information about vestibulospinal inputs to axial motoneurons in mammals, providing a more comprehensive platform for future studies into the overall organization of vestibulospinal inputs and their role in regulating postural stability.