Disruption of Lateral Efferent Pathways: Functional Changes in Auditory Evoked Responses

The functional consequences of selectively lesioning the lateral olivocochlear efferent system in guinea pigs were studied. The lateral superior olive (LSO) contains the cell bodies of lateral olivocochlear neurons. Melittin, a cytotoxic chemical, was injected into the brain stem using stereotaxic coordinates and near-field evoked potentials to target the LSO. Brain stem histology revealed discrete damage to the LSO following the injections. Functional consequences of this damage were reflected in depressed amplitude of the compound action potential of the eighth nerve (CAP) following the lesion. Threshold sensitivity and N1 latencies were relatively unchanged. Onset adaptation of the cubic distortion product otoacoustic emission (DPOAE) was evident, suggesting a reasonably intact medial efferent system. The present results provide the first report of functional changes induced by isolated manipulation of the lateral efferent pathway. They also confirm the suggestion that changes in single-unit auditory nerve activity after cutting the olivocochlear bundle are probably a consequence of disrupting the more lateral of the two olivocochlear efferent pathways.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41379/1/10162_2002_Article_3018.pd

Enhancing knowledge on energy saving and insulation efficiency in buildings, by analysing thermal behaviour of a realistic small scale house

ISBN: 978-1-61804-368-9International audienceWithin the framework of sustainable development, a small scale genuine materials house (1/20 scale) andsurroundings has been designed. The realisation itself has already been described in a previous paper [1]. Due to themodular structure of the design, different types of measurements ate possible, like in a real house for educationpurposes. In this paper, a study of thermal behaviour of the small scale house is presented. Steady state andtransient behaviours with different double wall insulation are compared using temperature sensors and infraredthermal imaging. Results are discussed. As these results are positive, this 1/20 model kit will be used as aneducational tool for practical work in the near future

Design and construction of a portable Transcranial Magnetic Stimulation (TMS) apparatus for migraine treatment

International audienc

ÉLECTROVESTIBULOGRAPHIE PAR ÉLECTRODES À DISTANCE CHEZ L'ANIMAL

In order to produce synchronous detectable responses in the vestibular pathways, electrical stimuli (ES) were applied on guinea pigs cochleas, first during rest then during an angular acceleration. The difference between the signals recorded before and during rotation represented the variation of the response to ES induced by the kinetic excitation and thus represents an electro-vestibulographic (EVG) type of response. EVG responses recorded on the round window and on the vertex were made each of a main negative wave, with a rotation speed threshold of about 2 to 3°/s, with amplitudes proportional to the acceleration culminating respectively to 4 µV and 40 µV with latencies around 0.4 ms and 1.2 ms, which could be associated with the vestibular nerve and nucleus. These results, along with those related to post rotation responses and to selective cochlear and vestibular destructions, confirmed the vestibular specificity of EVG responses.Afin de produire dans les voies vestibulaires des réponses synchrones observables, des stimulations électriques (SE) sont appliquées sur la cochlée du cobaye, au repos puis au cours d'une accélération angulaire. La différence entre les signaux enregistrés avant et pendant la rotation reflète la variation de la réponse à la SE induite par l'excitation cinétique et représente donc une réponse de type électro-vestibulographique (EVG). Les réponses EVG enregistrées sur la fenêtre ronde et le vertex comportent chacune une onde principale négative, de seuil en vitesse voisin de 2 à 3°/s, d'amplitude proportionnelle à l'accélération, et, respectivement, culminant à 40 µV et 4 µV avec des latences voisines de 0,4 ms et 1,2 ms, qui peuvent être associées au nerf et au noyau vestibulaires. Ces résultats, ainsi que ceux relatifs aux réponses post rotatoires et à des destructions vestibulaires et cochléaires sélectives, confirment la spécificité vestibulaire des réponses EVG

DIFFERENTIAL EXPLORATION OF COCHLEAR AND VESTIBULAR RECEPTORS BY INTERACTION OF ARTIFICIAL AND NATURAL STIMULI

On utilise une excitation électrique du VIIIème nerf combinée à une stimulation soit acoustique soit vestibulaire (bruit blanc ou accélération angulaire horizontale respectivement) pour extraire des réponses exemptes d'artefact, de spécificité soit cochléaire, soit vestibulaire. Chez le cobaye, la réponse Electrique-Vestibulaire (PAEV) apparaît comme une onde monophasique d'une amplitude de quelques dizaines de microvolts et d'une latence de l'ordre de 0,3 ms, par opposition à la réponse électrique-cochléaire (PAEC), couramment polyphasique et d'une amplitude de plusieurs centaines de microvolts. Schematiquement, le PAEV disparaît après destruction sélective des récepteurs vestibulaires (PAEC inchangé) alors qu'il se maintient après traitement cochléotoxique (disparition du PAEC), en accord avec les observations histologiques ultérieures. Les autres caractéristiques physiologiques des réponses confirment l'aptitude de la technique à dériver des composantes spécifiquement cochléaire et vestibulaire.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 a 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

Assessing the Firing Properties of the Electrically Stimulated Auditory Nerve Using a Convolution Model

The electrically evoked compound action potential (eCAP) is a routinely performed measure of the auditory nerve in cochlear implant users. Using a convolution model of the eCAP, additional information about the neural firing properties can be obtained, which may provide relevant information about the health of the auditory nerve. In this study, guinea pigs with various degrees of nerve degeneration were used to directly relate firing properties to nerve histology. The same convolution model was applied on human eCAPs to examine similarities and ultimately to examine its clinical applicability. For most eCAPs, the estimated nerve firing probability was bimodal and could be parameterised by two Gaussian distributions with an average latency difference of 0.4 ms. The ratio of the scaling factors of the late and early component increased with neural degeneration in the guinea pig. This ratio decreased with stimulation intensity in humans. The latency of the early component decreased with neural degeneration in the guinea pig. Indirectly, this was observed in humans as well, assuming that the cochlear base exhibits more neural degeneration than the apex. Differences between guinea pigs and humans were observed, among other parameters, in the width of the early component: very robust in guinea pig, and dependent on stimulation intensity and cochlear region in humans. We conclude that the deconvolution of the eCAP is a valuable addition to existing analyses, in particular as it reveals two separate firing components in the auditory nerve