186,171 research outputs found
A new tool for investigating the functional testing of the VOR
No full textPeripheral vestibular function may be tested quantitatively, by measuring the gain of the angular vestibulo-ocular reflex (aVOR), or functionally, by assessing how well the aVOR performs with respect to its goal of stabilizing gaze in space and thus allow to acquire visual information during the head movement. In recent years, several groups have developed clinical and quantitative approaches to functional testing of the vestibular system based on the ability to identify an optotype briefly displayed on screen during head rotations.Although the proposed techniques differ in terms of the parameters controlling the testing paradigm, no study has thus far dealt with understanding the role of such choices in determining the effectiveness and reliability of the testing approach. Moreover, recent work has shown that peripheral vestibular patients may produce corrective saccades during the head movement (covert saccades), yet the role of these eye movements towards reading ability during head rotations is not yet understood. Finally, no study has thus far dealt with measuring the true performance of their experimental setups, which is nonetheless likely to be crucial information for understanding the effectiveness of functional testing approaches. Thus we propose a new software and hardware research tool allowing the combined measurement of eye and head movements, together with the timing of the optotype on screen, during functional testing of the VOR based on the Head Impulse Test (HIT). The goal of such tool is therefore that of allowing functional testing of the VOR while collecting the experimental data necessary to understand, for instance, a) the effectiveness of the covert saccades strategy towards image stabilization, b) which experimental parameters are crucial for optimizing the diagnostic power of the functional testing approach, and c) which conditions lead to a successful reading or an error trial
A role for NMDAR-dependent cerebellar plasticity in adaptive control of saccades in humans
No full textBackground Saccade pulse amplitude adaptation is mediated by the dorsal cerebellar vermis and fastigial nucleus. Long-term depression at the parallel fibre-Purkinjie cell synapses has been suggested to provide a cellular mechanism for the corresponding learning process. The mechanisms and sites of this plasticity, however, are still debated. Objective To test the role of cerebellar plasticity phenomena on adaptive saccade control. Methods We evaluated the effect of continuous theta burst stimulation (cTBS) over the posterior vermis on saccade amplitude adaptation and spontaneous recovery of the initial response. To further identify the substrate of synaptic plasticity responsible for the observed adaptation impairment, subjects were pre-treated with memantine, an N-methyl-D-aspartate receptor (NMDAR) antagonist. Results Amplitude adaptation was altered by cTBS, suggesting that cTBS interferes with cerebellar plasticity involved in saccade adaptation. Amplitude adaptation and spontaneous recovery were not affected by cTBS when recordings were preceded by memantine administration. Conclusion The effects of cTBS are NMDAR-dependent and are likely to involve long-term potentiation or long-term depression at specific synaptic connections of the granular and molecular layer, which could effectively take part in cerebellar motor learning
After Effects of Cerebellar Continuous Theta Burst Stimulation on Reflexive Saccades and Smooth Pursuit in Humans
No full textThe use of cerebellar repetitive transcranial magnetic stimulation has been attempted for perturbing reflexive and voluntary eye movements, but discrepancies are seen between the results of distinct studies possibly due to the different stimulation sites, intensities, and paradigms. We describe the after effects of 20 and 40 s continuous Theta Burst Stimulation (cTBS) as compared to sham stimulation, applied over the lateral cerebellar vermis and paravermis on Reflexive Saccades (RS) and Smooth Pursuit (SP) eye movements, recorded in the 30 min following stimulation. The experiments were carried out in eight healthy volunteers, and eye movements were recorded monocularly with video-oculography. The 40 s cTBS significantly increased the amplitude of ipsilateral RS and the acceleration of the ipsilateral SP, and this effect was detectable all over the 30-min recording period; 40 s cTBS did not modify the other parameters, namely the peak velocity, the duration and the latency of RS, and the latency and the velocity of SP. The 20 s cTBS was ineffective on all RS and SP parameters. Finally, we detected a significant quite-linear reduction of RS peak velocity over time, but this was independent from cTBS and was probably caused by fatigue. The effects of 40 s cTBS in our experiments mimic the disorder of ocular motility in Wallenberg's syndrome and could result from functional impairment of cerebellopontine pathways. This effect lasts 30 min at least, and can provide a useful framework for adaptive ocular motor studies
Dynamics of Learning in the Open Loop VORXIII Mediterranean Conference on Medical and Biological Engineering and Computing 2013
No full textWe present our preliminary results on motor adaptation of the angular vestibulo-ocular reflex (aVOR) in response to passive impulsive head rotations at constant acceleration (460 deg/s2). Human healthy subjects were repeatedly subjected to a 20 degrees yaw rotation (using a rotating chair) while they tried to maintain fixation on a visual target. We used an incremental velocity error signal in which target moved partially with the head, during rotations, causing adaptation of the initial eye velocity. We analyzed only the first 100 msec of the aVOR, i.e. the open loop portion of the response. In order to better understand the multiple-timescales dynamics of motor learning subjects were adapted to a aVOR gain reduction period followed by a shorter reverse adaptation block of trials, and a subsequent no-error feedback period which caused a recovery toward the initially adapted state. Adaptation mechanisms have been successfully described using a two hidden states model, in which a fast state learns quickly from motor error, but has poor retention, and a slow state that learns slowly but has a stronger retention. We modeled our data using such two-states model finding an underestimation of the spontaneous recovery trend
A device for the functional evaluation of the VOR in clinical settings
No full textWe developed the head impulse testing device (HITD) based on an inertial sensing system allowing to investigate the functional performance of the rotational vestibulo-ocular reflex (VOR) by testing its gaze stabilization ability, independently from the subject’s visual acuity, in response to head impulses at different head angular accelerations ranging from 2000 to 7000 deg/s2. HITD was initially tested on 22 normal subjects, and a method to compare the results from a single subject (patient) with those from controls was set up. As a pilot study, we tested the HITD in 39 dizzy patients suffering, non-acutely, from different kinds of vestibular disorders. The results obtained with the HITD were comparable with those from the clinical head impulse test (HIT), but an higher number of abnormalities was detectable by HITD in the central vestibular disorders group. The HITD appears to be a promising tool for detecting abnormal VOR performance while providing information on the functional performance of the rotational VOR, and can provide a valuable assistance to the clinical evaluation of patients with vestibular disorders
P36. Using opioid-induced bilateral vestibular dysfunction to validate the Head Impulse Testing Device – Functional Test (HITD-FT)
No full textExtraction of Traditional COP-Based Features from COM Sway in Postural Stability Evaluation.
No full textPostural control during quiet standing is traditionally evaluated by analyzing CoP sway measured by using a force platform. However, recent proliferation of motion tracking systems made available an estimate of the CoM location. Traditional CoP-based measures presented in literature provide information about age-related changes in postural stability and fall risk. We investigated, on an age-matched group of subjects, the relationship between classical CoP-based measures computed on sway path and statistical mechanics parameters on diffusion plot, with those extracted from CoM time-series. Our purpose is to understand which of these parameters, computed from CoM sway, can discriminate postural abnormalities, in order to use a video tracking system to evaluate balance in addition to motor capabilities.
Development of an automatic evaluation system for balance assessment scales
No full textThe problem of a correct fall risk assessment is becoming more and more impelling with the increasing elderly population. However, despite this fact, no new tools have been developed to improve the ability to predict fall risk in individual patients and the clinical assessment procedures are based on subjective scoring of clinical balance scales.
This work documents our current effort to develop a novel method to inspect balance control through a system for the automatic evaluation of exercises drawn from balance assessment scales. Our aim is to overcome classical limits found in these scales i.e. limited granularity and inter-/intra-rater reliability, to obtain objective scores and more detailed information allowing to predict fall risk
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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