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Vertigo is an illusion of rotatory or linear movement that demonstrates a functional or lesional disturbance of the vestibular system, from periphery to central connections. According to the ANAES report (1997), benign paroxysmal positional vertical vertigo, vestibular neuronitis and Meniere's disease account for 40-50% of all mixed vertigo etiologies. Central etiologies may account for 20-40% of causes and 10-40% remain more difficult to classify, and are usually classified under the term of "peripheral vestibulopathy." These include vertigo due to neurovascular compression syndrome of the VIIIth nerve. Clinical manifestations, differential diagnosis, and treatment of the main etiologies of vertigo will be developed in this chapter. A specific section will discuss the subject of neurovascular compression syndrome of the VIIIth nerve. Even though some publications should be challenged, it appears that neurovascular compression syndrome of the VIIIth nerve might explain some cases of vertigo or chronic instability, with or without cochlear signs. The diagnosis is difficult and must be established on multiple clinical, electrophysiological and radiological arguments. A therapeutic test with antiepileptic drugs is helpful. The treatment includes these drugs as a first option but may require a neurosurgical approach if medical treatment fails.

The nerve function of the VIIIth nerve is at risk during microvascular decompression (MVD) for hemifacial spasm (HFS). Intraoperative monitoring of brainstem auditory evoked potentials (BAEPs) can be useful in decreasing the danger of hearing loss. This study assessed the intraoperative BAEP findings related to the surgical process to clarify the optimum maneuvers of MVD surgery to avoid hearing impairment.Hundred consecutive patients undergoing MVD for HFS with intraoperative BAEP monitoring were retrospectively reviewed. Patients were classified into four groups based on the greatest intraoperative latency prolongation and amplitude reduction of wave V of BAEP. Postoperative hearing function and surgical procedures including use of the brain retractor, preservation of arachnoid membrane along the VIIIth nerve, and duration of microscopic manipulation were analyzed in relation to the BAEP findings.Three patients complained of hearing loss after the surgery, but two had complete recovery and only one suffered permanent moderate hearing impairment. Longer duration of microscopic manipulation and greater use of the brain retractor tended to have negative effects on the BAEP findings, whereas preservation of arachnoid membrane along the VIIIth nerve had a positive effect. Statistical analysis showed significant difference in preservation of arachnoid membrane along the VIIIth nerve in Groups 2 and 4 (p = 0.013).Stretching of the VIIIth nerve should be avoided to prevent postoperative hearing impairment. Adequate exposure of the lower cranial nerve roots and lateral medulla oblongata from the caudal side without using the brain retractor gives enough space for decompression with minimum stretching of the VIIIth nerve. Maximum preservation of the arachnoid membrane along the VIIIth nerve and shortening of the duration of microscopic manipulation may help in avoiding postoperative hearing impairment.

Background: A case of tinnitus possibly due to vascular loop compression of VIIIth nerve is presented. Case presntation: A33-years old female suffers from tinnitus beginning 4 years ago. An extensive clinical and laboratory investigation did not reveal any abnormal finding except MRI signs of a vascular loop pressure of VIIIth nerve. Discussion: The medication did not help the patient and she refused to undergo surgery. We present the arguments of the causal relationship of the findings on MRI and symptoms of the patient. Conclusion: Tinnitus due to vascular pressure is a syndrome which should be considered in differential diagnosis in case of tinnitus.

The teleost Mauthner (M-) cell mediates a sound-evoked escape behavior. A major component of the auditory input is transmitted by large myelinated club endings of the posterior VIIIth nerve. Paradoxically, although nerve stimulations revealed these afferents have mixed electrical and glutamatergic synapses on the M-cell's distal lateral dendrite, paired pre- and postsynaptic recordings indicated most individual connections are chemically silent. To determine the sensory information encoded and the relative contributions of these two transmission modes, M-cell responses to acoustic stimuli in air were recorded intracellularly. Excitatory postsynaptic potentials (EPSPs) evoked by both short 100- to 900-Hz “pips” and longer-lasting amplitude- and frequency-modulated sounds were dominated by fast, repetitive EPSPs superimposed on an underlying slow depolarization. Fast EPSPs 1) have kinetics comparable to presynaptic action potentials, 2) are maximal on the distal lateral dendrite, and 3) are insensitive to GluR antagonists. They presumably are coupling potentials, and power spectral analysis indicated they constitute a high-pass signal that accurately tracks sound frequency and amplitude. The spatial profile of the slow EPSP suggests both proximal and distal dendritic sources, a result supported by predictions of a multicompartmental model and the effects of AMPAR antagonists, which preferentially reduced the proximal component. Thus a second class of afferents generates a portion of the slow EPSP that, with sound stimuli, demonstrate that the dominant mode of transmission at LMCE synapses is electrical. The slow EPSP is a dynamic, low-pass representation of stimulus strength. Accordingly, amplitude and phase information, which are segregated in other systems, are faithfully represented in the M-cell.

The standard translabyrinthine approach for acoustic neuromas removal was introduced by W. House in 1964. After several years of experience the original translabyrinthine approach has been progressively modified into the current "enlarged" approach by extending the area of bone removal. This increased surgical field has made the translabyrinthine approach suitable for the removal of tumours of all sizes. We present our serie of 71 large (52) and giant (19) neuromas of the VIIIth nerve removed through a translabyrinthine approach between 1993 and 1998 at the ENT Department of Legnano.

Group delays of 2 f1-f2 distortion product otoacoustic emissions (DPOAEs) were determined using both f1- and f2-sweep paradigms in 24 normal-hearing subjects. These DPOAE group delays were studied in comparison with cochlear delays estimated from derived band VIIIth nerve compound action potentials (CAPs) and auditory brainstem responses (ABRs) in the same subjects. The center frequencies of the derived bands in the electrophysiological experiment were matched with the f2-frequencies in the DPOAE recording to ensure that DPOAEs and derived CAPs and ABRs were generated at the same places along the cochlear partition, thus allowing for a direct comparison. The degree to which DPOAE group delays are larger in the f2- than in the f1-sweep paradigm is consistent with a theoretical analysis of the so-called wave-fixed model. Both DPOAE group delays are highly correlated with CAP- and ABR-derived measures of cochlear delay. The principal result of this study is that "roundtrip" DPOAE group delay in the f1-sweep paradigm is exactly twice as large as the neural estimate of the "forward" cochlear delay. The interpretation of this notion in the context of cochlear wave propagation properties and DPOAE-generating mechanisms is discussed.

A micromachined silicon substrate sieve electrode was implanted within transected toadfish ( Opsanus tau) otolith nerves. High fidelity, single unit neural activity was recorded from seven alert and unrestrained fish 30 to 60 days after implantation. Fibrous coatings of genetically engineered bioactive protein polymers and nerve guide tubes increased the number of axons regenerating through the electrode pores when compared with controls. Sieve electrodes have potential as permanent interfaces to the nervous system and to bridge missing connections between severed or damaged nerves and muscles. Recorded impulses might also be amplified and used to control prosthetic devices.

Kluender, Lotto, and Jenison [J. Acoust. Soc. Am. 97, 2552–2567 (1995)] reported that overall stimulus amplitude can affect perception of the voicing contrast in syllable‐initial stops. Their results supported an hypothesis that a shift in the temporal pattern of neural firing from frequencies near F2 and F3 to F1 and f0 could signal voicelessness. The results of the current study undermine this ‘‘synchrony capture hypothesis.’’ The effect of amplitude (increased voiceless identifications with higher amplitude) maintains when there is no cutback in F1 during the quasiperiodic portion of the syllable and when stimuli are high‐pass filtered above the frequency of F1. In a further test of the hypothesis, two ten‐step series (/ba/–/pa/ and /ga/–/ka/) were created which maintained period voicing throughout the syllable (with F1 cutback signaling voicelessness). The energy just below the frequency of F2 and the energy above F1 were presented dichotically. Thus, at the periphery, there was no competition between frequencies near F2 and lower frequencies and, as a result, no chance for a change in neural temporal patterns. Subjects continued to label voicelessness as a function of overall amplitude. Alternative models of the encoding of voicelessness will be considered. [Work supported by NIDCD and NSF.]

Maturation of the cochlea and afferent auditory units is reflected by changes in VIIIth nerve compound action potential (CAP) parameters. We studied auditory nerve CAPs evoked by low-intensity stimuli in Mongolian gerbils (Meriones unguiculatus) ranging in age from 22 to 92 days after birth. The gerbil CAP development is characterized by marked changes in latency, threshold, and amplitude during the first few weeks of life. CAP latency and CAP threshold reach adult-like values at about 1 month of age. In contrast, the CAP amplitude continues to grow in size even after 2 months. This dichotomy suggests that the development of afferent auditory nerve function in the gerbil is preceded by maturation of the mechanical processes of the middle ear and cochlea.

Most physiological and behavioral studies of the Mauthner cells have used the goldfish and a few other fish from the superorder Ostariophysi, series Otophysi (= otophysans). We first provide some background and recent findings on the Mauthner cells of otophysan fish and then compare this information to that known about the Mauthner cells in certain non-otophysan fish. These comparisons are meant to provide the impetus for a comparative approach to understanding the role of the Mauthner cells in behavior.

The gold standard for control of vertigo in vestibular disorders is the translabyrinthine total VIIIth nerve section. This procedure is recommended for patients disabled by vertigo when there is severe or total loss of hearing in the involved ear. The procedure is associated with a low morbidity rate and insures a total loss of vestibular function in the operated ear.

An electrical excitation of the VIIIth nerve was used in combination with either an acoustic or a vestibular stimulus (white noise or horizontal angular acceleration respectively) to derive artefact-free responses with either cochlear or vestibular specificity. In the guinea pig, the Electrical-Vestibular response (EVAP) appeared to be monophasic with it few tens microvolts amplitude and a typical 0.3 ms latency, as opposed to the electrical-cochlear response (ECAP), a commonly polyphasic potential with a few hundreds microvolts amplitude. Schematically, the EVAP was abolished after a selective destruction of vestibular receptors (ECAP unchanged) while a cochleotoxic treatment left the EVAP unchanged (ECAP abolished), in accordance with further histological observations. Other physiological characteristics of the responses confirmed the ability of the technique to separate cochlear and vestibular specific components.

To report on the outcomes of cochlear implantation (CI) in a child with cochleovestibular nerves (CVN) hypoplasia.Retrospective case review.Tertiary referral center, University hospital.An 18-month-old child with profound bilateral congenital hearing loss and bilateral hypoplasia of the CVN at imaging.Left CI at age 29 months with a Nucleus Contour device (Cochlear Ltd., Lane Cove, New South Wales, Australia) after unsatisfactory results of hearing aid use for 10 months.Speech perception tests, behavioral observation, electrophysiologic tests, and cognitive evaluation.Although the child scores poorly in every perceptive category with the CI alone, the device greatly enhances his speech understanding with the hearing aid in the opposite ear. In the bimodal condition, his words and sentences identification, recognition, and comprehension far exceed the monaural figures. The Meaningful Auditory Integration Scale (MAIS) tests reaches a score of 26/40, and the MacArthur's questionnaires confirm the improvement of language production and comprehension. These results became noticeable after 5 to 6 months and continued to improve up to the 10th month. The child's cognitive scores and overall performance competences greatly benefit from the CI, with the mental age overcoming the chronological age.We can confirm the chance of achieving satisfactory results by CI even when the imaging of CVN is doubtful and the electrophysiological tests are disappointing. In our experience, a CI in Type IIb dysplasia of the CVN is a feasible option, provided that the candidate shows some responses at aided audiogram and at least minimal signs of language development. Adequate counseling is necessary for these children because the expected outcome is somewhat lower than that of their deaf peers with normal appearance of the nerves.

Hamartomas of the cerebellopontine angle or internal auditory canal are very rare and only four cases have been reported. We report an unusual case of a glioneural hamartoma of the VIIIth nerve with clinical, radiological and audiometric similarity with vestibular schwannoma.

To evaluate the applicability of vestibular-evoked myogenic potentials (VEMPs) in the diagnostics, intraoperative monitoring, and postoperative follow-up of patients in otoneurosurgery.A prospective study of patients who underwent either cochlear implantation (CI, n = 18) or were diagnosed with an acoustic neuroma (AN, n = 9) or with neuro(micro)vascular compression of the VIIIth nerve (NVC, n = 27) in the period 2002 to 2004. The follow-up was 1 year for all patients.A tertiary-referral unit.VEMPs could be recorded in 64% of all patients before CI and in 22% after surgery. The patients with AN had normal VEMPs in 22% of all cases when first diagnosed. Normal VEMPs were found in 37% of those patients with NVC. From the 5 AN patients who had to be operated, only 1 had intact VEMPs after surgery. In contrast, after microvascular decompression all patients (4) had normal VEMPs.VEMPs are helpful in diagnosing patients with vertigo to better identify saccular defects. They are highly sensitive in the early diagnosis of retrocochlear lesions.VEMPs can help to reliably identify patients with a retrocochlerar lesion at an early stage and can be used in intraoperative, neurophysiological monitoring.C-4.

Responses to free-field sound of 401 fibers from the VIIIth nerve of the grassfrog, Rana temporaria, are described. The spontaneous activities of the fibers ranged from 0 to 75 spikes/s, showing only weak correlation with frequency or sensitivity of the fibers. The highest spontaneous activities were approximately twice as high as reported previously for frogs. Best frequencies ranged from 100 to 1600 Hz and thresholds ranged from 21 to 80 dB SPL. The median dynamic range was 20 dB and the slopes of the rate-level curves ranged from 5 to 20 spikes/(s-dB). Most of the units showed post-excitatory suppression (PS) of their spontaneous activity. The duration of PS increased with sound level, also in fibers showing a decrease in firing rate at high intensities. Most fibers showing one-tone suppression did not show PS at their best suppression frequencies. Strong suppression was observed also in very phasic cells giving one spike per stimulation. Therefore, the mechanism underlying PS is probably different from that underlying adaptation. The sharpening of the neural encoding of temporal parameters and the strong encoding of sound offset as well as onset caused by PS very likely is biologically important. Udgivelsesdato: 1998-May

We studied whether same-frequency contralateral tones of 65 dB pSPL (peak Sound Pressure Level) suppress the VIIIth nerve compound action potential (CAP) evoked by 40–45 dB pSPL tone pips in the Mongolian gerbil from 22 to 92 days after birth (DAB). The primary stimuli were tone pips of 1, 2, 4, 8, and 10 kHz; only the 1 kHz CAP amplitude was suppressed significantly by tones of the same frequency. The suppression was seen at 22 DAB, and underwent little relative change with development.

Facial nerve neurinomas are rare in comparison to other schwannomas of the base of the skull, notably and especially neurinomas of the VIIIth nerve, but also tumors of mixed nerves expressed in the jugular foramen on in the cervical region. Recent observations have spectacularly illustrated the extremely polymorphous character of the symptomatology encountered and the value of the classification proposed by Sterkers et al. in 1986 [5]. The following is a brief review of that classification.

1. Responses of 73 fibers to dorso-ventral vibration were recorded in the saccular and utricular branchlets of Rana pipiens pipiens using a ventral approach. The saccular branchlet contained nearly exclusively vibration-sensitive fibers (33 out of 36) with best frequencies (BFs) between 10 and 70 Hz, whereas none of the 37 fibers encountered in the utricular branchlet responded to dorso-ventral vibrations. 2. Using a dorsal approach we recorded from the VIIIth nerve near its entry in the brainstem and analyzed responses to both sound and vibration stimuli for 65 fibers in R. pipiens pipiens and 25 fibers in Leptodactylus albilabris. The fibers were classified as amphibian papilla (AP), basilar papilla (BP), saccular or vestibular fibers based on their location in the nerve. Only AP and saccular fibers responded to vibrations. The AP-fibers responded to vibrations from 0.01 cm/s2 and to sound from 40 dB SPL by increasing their spike rate. Best frequencies (BFs) ranged from 60 to 900 Hz, and only fibers with BFs below 500 Hz responded to vibrations. The fibers had identical BF's for sound and vibration. The saccular fibers had BFs ranging from 10 to 80 Hz with 22 fibers having BFs at 40–50 Hz. The fibers responded to sound from 70 dB SPL and'to vibrations from 0.01 cm/s2. 3. No differences in sensitivity, tuning or phase-locking were found between the two species, except that most BP-fibers in R. pipiens pipiens had BFs from 1.2 to 1.4 kHz, whereas those in L. albilabris had BFs from 2.0 to 2.2 kHz (matching the energy peak of L. albilabris' mating call). 4. The finding that the low-frequency amphibian papilla fibers are extremely sensitive to vibrations raises questions regarding their function in the behaving animal. They may be substrate vibration receptors, respond to sound-induced vibrations or bone-conducted sound.

1) The peripheral origins of vibration-sensitive VIIIth nerve fibers in European grassfrogs (Rana temporaria) were investigated by recording from individual nerve branchlets within the inner ear. Furthermore, the fibers' responses to both pulsed and continuous, dorsoventral, sinusoidal vibrations were studied. 2) Vibration-sensitive fibers were found in both the anterior and posterior branch of the VIIIth nerve. 3) No vibration-sensitive fibers were found in the lagenar nerve. 4) The vibration-sensitive fibers in the posterior branch probably innervated the amphibian papilla and many of these fibers also responded to low-frequency sound. 5) The vibration-sensitive fibers in the anterior branch probably innervated the sacculus and the utriculus. 6) Hence, the grassfrog has at least two, and probably three, vibration-sensitive organs in the inner ear. 7) All fibers had V-shaped vibrational tuning curves. In the posterior branch best frequencies (BFs) ranged from 10 to 300 Hz, in the anterior branch from 10 to 100 Hz. In the posterior branch spike-rate thresholds at BF ranged from 0.04 to 1.28 cm/s2, in the anterior branch from 0.02 to 1.28 cm/s2. All fibers showed strong synchronization to the stimulus waveform, particularly at low frequencies.

This study attempted to develop a test which would be specific for endolymphatic hydrops. It is based upon the hypothesis that increased pressure in the scala media will alter the stiffness of the basilar membrane and hence increase the speed of the travelling wave. Auditory brainstem-derived responses were used to measure the basilar membrane travelling wave velocity in normals and to take the equivalent measures in Meniere's patients. Ten normally hearing subjects and 20 Meniere's patients were tested. The data for the Meniere's group showed that the travelling wave velocities were within normal limits at all frequencies tested, except 5.7 kHz where the travelling wave velocity greatly exceeded that of the normal group. A theoretical possibility that these findings may be the result of damaged and broadened VIIIth nerve tuning curves is discussed but travelling wave measures and psychophysical tuning curve measurements on the Meniere's group, normals and noise-induced hearing loss (NIHL) cases showed that this was not a significant factor. The data indicate that this technique can detect endolymphatic hydrops and a short duration clinical procedure has been devised.

Edited by Reinhard Konig, Peter Heil, Eike Budinger, Henning Scheich. Published by Lawrence Erlbaum Associates, New Jersey, 2005, £62.95 (hardcover), pp 493. ISBN 0-8058-4938-6 A spirit who hears me tapping/The five-sensed cane of mind Amid such unguessed glories/That I am worse than blind. H Kemp, Blind , 1919 Most clinical neurologists scarcely spare a thought for the auditory brain: it is what takes over where the VIIIth nerve ends, and if they think of it at all, it is probably in connection with such exotic maladies as cortical deafness or curios like musical hallucinations. But …

Auditory brain stem responses (ABR) of 61 patients with tumors of the VIIIth nerve or cerebellopontine angle were analyzed for latency of the I-III, III-V, and I-V interwave intervals. Of the 61 patients, 16 yielded ABR records with repeatable waves I, III, and V so that interwave intervals could be measured. Results indicate that not only is the I-III interval often abnormal, but in almost 50% of the cases the III-V interval is also extended. Additional analysis included comparing a group of subjects with cochlear lesions with the 16 patients with VIIIth nerve tumors. These findings indicated a higher degree of specificity than sensitivity for the ABR interwave measurement. These findings, as well as additional analyses, are discussed.

Electrical stimulation of one VIIIth nerve evoked simple spike activity in Purkinje cells located on either side of the cerebellum. This cellebullar output was delayed by ca. 10 ms with respect to its mossy fiber-parallel fiber input. The onset of the cerebellar output occurs on the average simultaneously on either side of the corpus cerebelli. The delay is explained by slowly rising EPSPs in PC induced by primary afferent and by second and higher order vestibular fibers. The latter inputs are stronger and terminate ipsi- and contralaterally in the granular layer.

Of the 441 patients of Meniere's disease treated at the Neurotology Clinic of Toranomon Hospital from 1969 to 1983, 330 were observed for a long time. The longest period of observation was 15 years.1. Changes of symptoms and functions1) Hearing: same. . 72%, improved. . 15%, worse. . 13%.2) Vertigo: no vertigo.. 57%, very mild dizziness 43/%.3) Caloric test: same. . 95%, worse. . 5%.2. Bilateral Meniere's disease appeared in 24 cases cases (5%).3.Therapy1) Conservative therapy2) Patients with frequent vertigo attacksWhen the glycerol test was positive, endolymphatic sac surgery was performed. When the glycerol test was negative and hearing was preserved, streptomycin sulfate infusion of the middle ear was performed. When the hearing impairment was severe, labyrinthectomy or VIIIth nerve section was done.

SummaryThe various categories of inner ear disorder are classified and those suitable for surgical treatment are defined. The importance of establishing a generally acceptable system of therapeutic efficiency and some of the means whereby this goal might be achieved are discussed. The results of operations on 55 patients with the presumptive diagnosis of Meniere's disease were analyzed between 2 and 12-years' post-operatively. The outcome, in terms of auditory and vestibular function, in 27 ears treated by decompression of the saccus endolymphaticus (using the Shambaugh technique) was compared with those in 28 ears having selective VIIIth nerve section. Although the latter procedure provided better control of vertigo, there was no difference between either group with regard to preservation of hearing, nor was there any evidence from this study that either operation did anything to alter the progressive hearing loss which is characteristic of Meniere's disease. Nevertheless, because of failure of non-invas...

Brainstem auditory evoked potentials (brainstem AEPs) were simultaneously recorded from 13 scalp and earlobe electrodes from normal subjects employing a noncephalic reference. The scalp distributions of the individual components (waves I-V) were presented as isopotential maps with the use of a topographic computer display system. Binaural clicks produced symmetrically distributed brainstem AEPs over the scalp. With monaural stimulation, the topography of the responses differed in locus of maximum amplitude for each of the components, suggesting that different generators are involved in the production of these components (for example, wave V is of maximal amplitude with the shortest peak latency over the contralateral frontal area). Wave I was the only component that reversed its polarity according to electrode locations. Other waves were positive over the scalp and earlobes in confonnity with the concept that they are volume conducted, far field potentials. Brainstem AEPs in subjects with lesions ...

A 67-year-old woman developed clinic al findings consistent with herpes zoster of the left ear, localized encephalitis and meningitis. These signs included herpes of the left external ear and soft palate, VIIth and VIIIth nerve disfunction, ataxia and electro-nys-tagmographic (ENG) abnormalities ; defective opto-kinetic nystagmus and saccadic pursuit towards the right.Treatment with adenin arabinoside (Ara-A) resulted in rapid improvement.The importance of CSF examination including cell counts and CSF-IgG index, ENG and EEG was emphasized.

The ability of auditory fibers in the anuran's VIIIth nerve to regenerate back into the central nervous system after their axons have been served was studied electrophysiologically and anatomically. Single unit recordings in the regenerated portion of the nerve indicate that: (1) fibers from both the amphibian and basilar papillae regenerate; (2) tuning curves of regenerated fibers, as in normal fibers, are 'V' shaped and retain their sharp frequency selectivity; (3) latency and threshold measurements of regenerated fibers are similar to values obtained in intact nerves. Filling the posterior branch of the regenerated VIIIth nerve with horseradish peroxidase indicates that fibers in this branch remain together within the nerve during regeneration and succeed in terminating in their correct target nuclei and no others.

1. Measurements of each of the inner ear sensory areas are reported and compared for various vertebrates. These indicate:a. 5:5 and 6:4 ratios are most common in comparing the total pars superior sensory area of the inner ear with the total pars inferior area;b. 7:3 to 2:8 ratios exist, in comparing the canal type with the macular type areas, which appear to be related to the equilibratory demands made upon the organism;c. that, in comparing cochlear type with saccular type areas, the tailless amphibians exhibit a surprisingly high value for the former;d. that in some forms the crista horizontalis is larger than the average of the two vertical cristae, possibly associated with the mode of locomotion;e. that the macula sacculi, throughout vertebrates, is of considerable size, as is the macula lagenae (where present);f. that there is a great actual and relative variation in the size of the papilla basilaris (organ of Corti), particularly among reptiles;g. that it is the size of the papilla amphibiorum which...

Summary Auditory evoked potentials to ‘clicks’ were averaged from the scalps of litters of anesthetized rat pups and kittens throughout neonatal development. The potentials were shown to be from the brain stem auditory system, VIIIth nerve to inferior colliculus. At a fixed intensity and rate, peak latencies of the waves shortened with increasing age, while inter-litter variability decreased. The latencies of early waves shortened to adult values at younger ages than later waves. Increasing the intensity of stimulus at any age caused reduced latency of all of the waves; sometimes, the pattern of latencies seen at a younger age could be duplicated at an older age with a decreased intensity. Increasing the stimulus rate reduced the size of the waves, and there was return to control levels after 100 stimuli/sec in rat pups, adult rats, and cats, but not in kittens. The results are consistent with the hypothesis that significant limitations in both the immature and mature auditory system, as measured by peak latencies, occur before the VIIIth nerve. Several of the parameters studied can serve as a measure of ‘maturation’ in the auditory system, but at some ages one measure may be ‘immature’ when another is ‘mature’.

We have been particularly concerned with the large number of patients with confirmed retrocochlear lesions who have demonstrated cochlear test results on audiological evaluation. The literature is replete with information suggesting that the patient with a tumor of the VIIIth nerve will demonstrate the classical signs of significant reduction in auditory speech discrimination, abnormal tone decay, lack of loudness recruitment, negative SISI scored and Bekesy tracings classifiable as either type III or type IV. We feel it is safe to say that one rarely encounters such a clearcut picture.In this paper we discuss the audiologic data for a series of patients recently evaluated in our department. All these patients demonstrated only cochlear findings on audiological evaluation, yet all patients had surgically confirmed VIIIth nerve tumors.

Single cell activity was recorded extracellularly from neurones in cat's abducens nuclei in unanesthetized, decerebrate preparations. Two types of neurones were found. i) The motoneurones (type IIA) increased their firing linearly or exponentially to contralateral constant angular accelerations and decreased firing to ipsilateral rotation. The increased frequency was maintained at a constant level without any sign of adaptation. This constant level of maximum frequency was proportional to the logarithm of the acceleration applied. No significant differences of the frequency responses of tonic and silent motoneurones were found. The conduction velocities of the axons of spontaneously firing type IIA cells were slower than in silent neurones. Electrical stimulation of the contralateral VIIIth nerve led to activation of the type IIA cells; stimulation of the ipsilateral nerve resulted in inhibition of both spontaneous discharge and antidromic invasion of the motoneurones. ii) The type IA units increased their firing rate to ipsilateral rotation and ceased to discharge in response to contralateral rotation. They never were excited antidromically by stimulation of the VIth nerve. However, they were excited by stimulation of the ipsilateral VIIIth nerve. Their possible functional role in the vestibulo-ocular system was discussed.

The primordium of the VIIIth cranial ganglion (otic vesicle) was extirpated on the right side of 428 embryos of Ambystoma maculatum at stage 27. Mauthner's cell (MC) develops in close association with the VIIIth nerve roots and to a lesser degree with VIIth lateral-line roots. The primary objective of the experiments was to record from a large series of animals the number of cases in which MC failed to differentiate in the absence of VIIIth root fibers. In addition, all embryos were separated (stages 3, 5, 9) into various groups and maintained continuously at different constant temperatures (5°, 8°, 10°, 14°, 18°C) until operation. The various temperature groups were then compared among themselves for any constant or significant differences with regard to the suppression of MC on the operated side. Animals were examined at stage 46. The VIIIth root fibers were completely absent in every case on the operated side. Although the VIIth lateral-line ganglia were present in all animals, root fibers failed to develop in 173 cases. This afforded an opportunity to study the influence of VIIth lateral-line roots upon the differentiation of MC, as well as the influence of VIIIth roots. Mauthner's cell was absent in 119 cases (27.8%). In 55 of these cases only VIIIth root fibers were absent; in 64 cases both VIIIth and VIIth roots were missing. The importance of VIIIth root fibers in influencing the differentiation of MC, therefore, is obvious since in 46% of those cases in which MC failed to develop absence of the VIIIth root was the only deviation from normal. The presence or absence of MC correlated with the presence or absence of VIIth lateral-line roots gives a relatively high Chi-square value of 11.461. The temperature series data are inconclusive in demonstrating a critical or optimal thermal effect upon the sequential steps affecting the differentiation of MC. If the time in early development when temperature differentials were applied is ignored, there are no consistent or significant differences among the temperature groups with regard to the suppression of MC in the absence of the VIIth–VIIIth root complex. On the other hand, if only those animals are considered that were separated at stage 9 (the majority of the animals), then there is a low degree of correlation (significance slightly above the 1% level) between greater suppression of MC in the 8° groups as opposed to lesser suppression in the 14° groups. These results on temperature influence are in need of further experimentation and analysis.

Six subjects with VIIIth nerve audiometric profiles tracked thresholds for periodically interrupted tones on a Bekesy audiometer. When on-time was held constant and off-time was varied, a critical off-time (COT) appeared at one or more frequencies in each subject.

According to Witmaack (1911), division of the VIIIth nerve in the cat results in widespread degeneration of the cochlear neurones peripheral to the point of section; the morphological integrity of all other cochlear elements being maintained. These findings have been confirmed by later observers (Kaida 1931; Hallpike and Rawdon-Smith 1934 b ), who have in addition shown that these results require for their production the avoidance of damage to the cochlear vessels, which is found to bring about a generalized necrosis of the contents of the internal ear. A study of the electrical response of the internal ear (cochlear component of the Wever and Bray phenomenon) found to occur in the cochlea of a cat denervated in the manner described, has been the subject of a previous publication (Hallpike and Rawdon-Smith 1934 b ). In this, absence of electrical response was found to occur in a cochlea morphologically normal apart from the elimination of the neural elements. The results of a further series of observations upon these lines are now available and form the subject of the present paper.

A variety of psychoacoustic procedures was administered to three subjects—one with normal hearing, one with cochlear disorder, and one with VIIIth nerve disorder. Auditory tasks included discrimination of loudness, pitch, and temporal order; critical off-time; and speech intelligibility. A number of differences in response pattern were noted. Both theoretical and applied implications are discussed.

In precollicular decerebrate cats, stimulation of the VIIIth cranial nerve increases the discharge of muscle spindle receptors of the gastrocnemius muscle of the cat at low frequencies of stimulation (2–25 pulses/sec). Extrafusal contraction is induced only at higher frequencies of stimulation (16–100 pulses/sec). Both spindle receptor acceleration and extrafusal contraction increase with increase in frequency of VIIIth nerve stimulation to an optimum value at about 100 pulses/sec and then fall progressively with further increase in frequency of stimulation from 200 to 500 pulses/sec. Effects similar to those from the VIIIth cranial nerve are obtained from the medial and descending vestibular nuclei.

Examination of click-evoked VIIIth nerve actio potentials (AP) recorded from the round windw of anesthetized rats at ages of one, six, 12, 18 and 24 months reveals that: 1. Visual detectio levels for AP increase by 17.5 db from six to 24 months of age; 2. N1 voltage increases to a maximum at six or 12 months, depending on click level, and then declines to 24 months; 3. N2 voltage increases from one to six months but does not show a regular decline thereafter: 4. The voltage of the positive peak separating N1 from N2 shows irregular age changes; 5. N1 latency does not change significantly with advancing age; and 6. N1-N2 latency is reduced between one and 12 months but remains relatively stable thereafter.

The course and distribution of the vestibulospinal tract in the toad have been studied in silver-impregnated sections following electrolytic lesions of the terminal nuclei of the VIIIth cranial nerve. The tract originates from the ventral, vestibular nucleus of the VIIIth nerve and descends bilaterally in the ventral funiculi throughout the whole length of the spinal cord. Contralateral fibers are less numerous than ipsilateral and cross the midline in the caudal medulla oblongata. Some fibers cross in the spinal gray matter ventral to the central canal.The vestibulospinal fibers terminate in the ventromedial region of the ventral horn which harbors the medial column of motoneurons, innervating the axial musculature. Silver-impregnated sections suggest that some fibers might terminate on the cell bodies and proximal dendrites of these motoneurons. Preliminary electron microscopical observations, however, confirm only the presence of degenerating boutons in the neuropile of this region.Short comment has been devoted to other descending fiber systems which were observed following hemisection of the high cervical cord.