Assessment of Utricular Nerve, Hair Cell and Mechanical Function, in vivo.

Vestibular research currently relies on single response measures such as ex vivo hair cell and in vivo single unit recordings. Although these methods allow detailed insight into the response properties of individual vestibular hair cells and neurons, they do not provide a holistic understanding of peripheral vestibular functioning and its relationship to vestibular pathology in a living system. For this to take place, in vivo recordings of peripheral vestibular nerve, hair cell and mechanical function are needed. The previous inability to record vestibular hair cell responses stemmed from a difficulty in accessing the vestibular end-organs and stimulating them in isolation of the cochlea. To circumvent this, we developed a ventral surgical approach, removing the cochlea, to provide full access to the basal surface of the utricular macula. This allowed functional and mechanical utricular hair cell recordings, alongside gross utricular nerve responses. Recordings were performed in anaesthetized guinea pigs using Bone Conducted Vibration (BCV) and Air Conducted Sound (ACS) stimuli, providing a clinical link to vestibular reflex testing. We have thus far performed experiments involving: 1) Selective manipulation of vestibular nerve function, using electrical stimulation of the central vestibular system. 2) Glass micropipette recordings from the basal surface of the macular epithelium, which provided a robust and localized measure of extracellular utricular hair cell function. 3) With the macular exposed, we have measured the dynamic motion of the macula using Laser Doppler Vibrometry, which was recorded alongside the hair cell and nerve response recordings. 4) We have used physiological and pharmacological experimental manipulations to selectively modulate utricular nerve, hair cell or mechanical function, demonstrating the ability to differentially diagnose the basis of peripheral vestibular disorders in the mammalian utricle. These tools allow for a more complete understanding of peripheral vestibular function and a first order perspective into clinical disorders effecting the otoliths

Gravito-Inertial Ambiguity Resolved through Head Stabilisation

It has been frequently observed that humans and animals spontaneously stabilise their heads with respect to the gravitational vertical during body movements even in the absence of vision. The interpretations of this intriguing behaviour have so far not included the need, for survival, to robustly estimate verticality. Here we use a mechanistic model of the head/otolith-organ to analyse the possibility for this system to render verticality ‘observable’, a fundamental prerequisite to the determination of the angular position and acceleration of the head from idiothetic, inertial measurements. The intrinsically nonlinear head-vestibular dynamics is shown to generally lack observability unless the head is stabilised in orientation by feedback. Thus, our study supports the hypothesis that a central function of the physiologically costly head stabilisation strategy is to enable an organism to estimate the gravitational vertical and head acceleration during locomotion. Moreover, our result exhibits a rare peculiarity of certain nonlinear systems to fortuitously alter their observability properties when feedback is applied

Parametric Study Of Short Latency Vestibular Evoked Potentials In Healthy Young Adults

The purpose of this study was to evaluate the feasibility of developing a novel approach of otolith assessment in humans. This approach used vestibular short-latency evoked potentials (VsEP) to evaluate some fundamental characteristics of VsEP responses in healthy young adults. Currently, measures for direct assessment of the otoliths are non-existent, as vestibular evoked myogenic potentials (VEMPs) rely on neck muscle contraction for cVEMPs or are a reflection of the vestibulo-ocular reflex (VOR) for oVEMPs, rather than the otoliths themselves (Fujimoto, Suzuki, Kinoshita, Egami, Sugasawa, & Iwasaki, 2018). Stimuli consisted of bone-conducted vibrations elicited by a specialized vibrator (Bruel & Kjaer, model 4810; B&K mini-shaker) attached to a power amplifier (B&K, model 2718) that causes linear acceleration movements of the skull. Standard reusable surface electrodes with the reference electrode placed on the forehead (Fpz), ground placed on the mastoid process of left ear (M2), and a (Lilly or Sanabel) wick electrode (placed as on the left tympanic membrane) were used to record early electrical activity (4ms). Data was collected and analyzed from 11 healthy young adults (6 males and 5 females) ranging in age from 19-39 years (mean: 23.1 years; SD: 6.9 years) who met the inclusion criteria for testing. Audiometric thresholds were tested to ensure normal hearing sensitivity (0.25-8 kHz; \u3c25 dB HL, bilaterally). A general analysis of the VsEPs was conducted through visual inspection of the waveforms and statistical analyses of the VsEP responses. The statistical analyses consisted of a series of one-way ANOVAs with repeated measures which included stimulus frequency (500 and 1000 Hz), intensity (115, 105, 95, & 85 dB SPL), along with masked (100, 90, & 80 dB HL) and unmasked conditions. VsEPs appear to be promising due to the simplicity of the test and ease of analysis - looking at waveforms without requiring active participation from participants. It would be necessary to complete testing on additional healthy participants to ensure that there continues to remain a consistency across all VsEP conditions regardless of participant; as this study showed, no large outliers were found across results for any of the participants tested in this study. It would also be beneficial to assess additional VsEP parameters (e.g., contralateral masking, additional stimulus and masking levels, varying durations, etc) in known individuals with specific otolith dysfunction to see if able to find such consistency across disordered group in the future before this assessment will be translatable into a clinical setting. Results of this study indicate that the amplitudes of the VsEPs are significantly impacted (p\u3c.05) by the intensity of the stimulus, regardless of the frequency tested, with the higher intensity having higher mean amplitudes than the lower intensities tested. On the other hand, the VsEP latencies remained consistent, regardless of the different frequencies, stimulus intensity, and masker levels assessed

Représentations de groupes de Lie et fonctionnement géométrique du cerveau

Two independent problems are considered in this thesis ; both feature non-commutative harmonic analysis−in other words, Lie group representation theory.The first problem was suggested by recent results from Neuroscience to Daniel Bennequin, who suggested it to me in turn. Our starting points are the receptive profiles of neurons in the primary visual cortex, and the geometrical properties of the maps describing how the neurons’ specializations are distributed on the surface of that part of the cortex. We recall that some remarkable properties of the "orientation maps" to be found in that cortical area are strikingly well reproduced by typical samples from Gaussian random fields on the Euclidean plane whose probability distribution is invariant under the Eucli- dean group, and whose samples probe an irreducible Plancherel factor of the quasi-regular representation of the Euclidean group on the space of functions on the Euclidean plane. We indicate that this interpretation makes it possible to build geometrical structures which call to mind, both qualitatively and qualitatively, the orientation maps of the visual cortex. Because the intervention of other groups is natural in the study of sensory information and motion planning, the construction of analogous structures on more general homogeneous spaces has an independent interest; we thus proceed to a study of invariant Gaussian random fields on riemannian homogeneous spaces, outline explicit constructions based on group representation theory (following Akiva N. Yaglom), and prove that when expressed an appropriate volume unit, the geometric measure of the zero-set of an invariant field depends only on the dimensions of the source and target spaces.The second problem was suggested by an old question from George W. Mackey and recent work by Nigel Higson ; the question was asked in 1975, and is internal to the representation theory of real reductive Lie groups. We describe a bijection between the tempered dual of a linear connected reductive Lie group and the unitary dual of its Cartan motion group. The second group is a contraction of the first, in the terminology of Inonü and Wigner ; in order to understand our bijection in terms of contractions of Lie groups, we consider an arbitrary irreducible tempered representation of the first group and introduce a family of contraction operators which make it possible to follow the individual smooth vectors (in an appropriate geometric realization for the representation) during the contraction ; we observe their convergence to the members of a carrier space for the representation of the Cartan motion group indicated by our bijection. We then use our results to give a new proof of the Connes-Kasparov conjecture in the case of linear connected reductive Lie groups, extending relatively recent work by Nigel Higson.This manuscript also contains a report on an attempt to use some matrix elements of unitary representations of the Galilei group in the study of electrophysiological recordings of the activity of Purkinje cells in the vestibulocerebellum of live (and alert) rats.Cette thèse étudie deux problèmes indépendants où l’analyse harmonique non-commutative, théorie des représentations de groupes de Lie, joue un rôle.Le premier problème a été suggéré par les neurosciences à Daniel Bennequin, qui me l’a proposé. Nous partons des profils récepteurs des neurones du cortex visuel primaire, et de la géométrie de la répartition des spécialités des neurones à la surface de cette aire corticale. Nous rappelons comment de remarquables propriétés des cartes d’orientation qu’on trouve dans cette aire corticale peuvent être reproduites par les tirages de champs aléatoires gaussiens invariants en loi dont les tirages explorent un facteur de Plancherel de la représentation quasi-régulière du groupe euclidien sur l’espace des fonctions sur le plan euclidien. Nous signalons que cette interprétation permet de construire, sur la sphère et sur le plan hyperbolique, des structures géométriques qui rappellent (qualitativement et quantitativement) les cartes d’orientation du cortex visuel. L’intervention naturelle d’autres groupes dans le traitement des informations sensorielles et la préparation du mouvement nous invite à envisager la construction d’objets analogues pour d’autres espaces homo- gènes comme une question mathématique d’intérêt indépendant. Nous étudions alors les champs aléatoires gaussiens invariants sur les espaces homogènes riemanniens, en donnant des constructions explicites issues de la théorie des représentations (d’après Akiva N. Yaglom) et en démontrant que dans une unité de volume adaptée, la mesure géométrique moyenne de l’ensemble des zéros ne dépend que des dimensions de la source et du but.Le second problème a été suggéré par George W. Mackey en 1975 ; il est interne à la théorie des représentations de groupes de Lie réductifs réels. Nous décrivons une bijection entre le dual tempéré d’un groupe de Lie linéaire connexe réductif et le dual unitaire de son groupe de déplacements de Cartan. Le second groupe est une contraction du premier, au sens d’Inonü et Wigner ; afin de comprendre la bijection précédente à l’aide de la notion de contraction, nous utilisons, pour toute représentation tempérée irréductible du premier groupe, une famille d’opérateurs de contraction qui permet de suivre le comportement des vecteurs lisses (dans une réalisation géométrique adaptée) au cours de la contraction et d’observer leur convergence vers la représentation du second groupe indiquée par notre bijection. Nous utilisons ensuite nos résultats pour donner une nouvelle preuve de la conjecture de Connes-Kasparov pour les groupes de Lie linéaires connexes réductifs, en suivant la méthode utilisée par Nigel Higson en 2008.Le manuscrit contient par ailleurs le récit d’une étude sur des données expérimentales issues d’enregistrements électrophysiologiques de l’activité de cellules de Purkinje dans le cervelet vestibulaire de rats vigiles, à l’aide d’éléments matriciels de représentations unitaires du groupe de Galilée