Stefano Ramat

University of Pavia | UNIPV · Dip. Ingegneria Industriale e dell'Informazione

Goal directed movements such as pointing and saccades have been shown to share similar neural architectures in spite of the different neuromuscular systems producing them. Such structure involves an inverse model of the actuator being controlled, which produces the commands innervating the muscles, and a forward model of the actuator, which predict...

Continuous theta-burst stimulation (cTBS) applied over the cerebellum exerts long-lasting effects by modulating long-term synaptic plasticity, which is thought to be the basis of learning and behavioral adaptation. To investigate the impact of cTBS over the cerebellum on short-term sensory-motor memory, we recorded in two groups of eight healthy su...

Measuring human movement has many useful applications ranging from fall risk assessment, quantifying sports exercise, studying people habits, and monitoring the elderly. Here, we present a versatile, wearable device based on a 9-degrees-of-freedom inertial measurement unit conceived for providing objective measurements of trunk or limb movements fo...

Human horizontal rotational vestibulo-ocular reflex (rVOR) has been extensively investigated: the horizontal semicircular canals sense yaw rotations with high-pass filter dynamics and a time constant (TC) around 5 s, yet the rVOR response shows a longer TC due to a central processing stage, known as velocity storage mechanism (VSM). It is generally...

Conductance-based models of reciprocally inhibiting burst neurons suggest that intrinsic membrane properties and postinhibitory rebound (PIR) determine the amplitude and frequency of saccadic oscillations. Reduction of the low-threshold calcium currents (I(T)) in the model decreased the amplitude but increased the frequency of the simulated oscilla...

Ambient Assisted Living is a concept that focuses on using technology to support and enhance the quality of life and well-being of frail or elderly individuals in both indoor and outdoor environments. It aims at empowering individuals to maintain their independence and autonomy while ensuring their safety and providing assistance when needed. Human...

Ambient Assisted Living (AAL) systems are designed to provide unobtrusive and user-friendly support in daily life and can be used for monitoring frail people based on various types of sensors, including wearables and cameras. Although cameras can be perceived as intrusive in terms of privacy, low-cost RGB-D devices (i.e., Kinect V2) that extract sk...

When the demands for visual stabilization during head rotations overwhelm the ability of the vestibulo-ocular reflex (VOR) to produce compensatory eye movements, the brain produces corrective saccades that bring gaze towards the fixation target, even without visual cues (covert saccades). What triggers covert saccades and what might be the role of...

Human Action Recognition (HAR) is a rapidly evolving field impacting numerous domains, among which is Ambient Assisted Living (AAL). In such a context, the aim of HAR is meeting the needs of frail individuals, whether elderly and/or disabled and promoting autonomous, safe and secure living. To this goal, we propose a monitoring system detecting dan...

The perirhinal cortex (PRC) is a polymodal associative region of the temporal lobe that works as a gateway between cortical areas and hippocampus. In recent years, an increasing interest arose in the role played by the PRC in learning and memory processes, such as object recognition memory, in contrast with certain forms of hippocampus-dependent sp...

Background Vestibular migraine (VM) is a relatively recently acknowledged vestibular syndrome with a very relevant prevalence of about 10% among patients complaining of vertigo. The diagnostic criteria for VM have been recently published by the Bárány Society, and they are now included in the latest version of the International Classification of He...

Automatic monitoring of daily living activities can greatly improve the possibility of living autonomously for frail individuals. Pose recognition based on skeleton tracking data is promising for identifying dangerous situations and trigger external intervention or other alarms, while avoiding privacy issues and the need for patient compliance. Her...

Continuous monitoring of frail individuals for detecting dangerous situations during their daily living at home can be a powerful tool toward their inclusion in the society by allowing living independently while safely. To this goal we developed a pose recognition system tailored to disabled students living in college dorms and based on skeleton tr...

Introduction: The vestibular implant could become a clinically useful device in the near future. This study investigated the feasibility of restoring the high-frequency dynamic visual acuity (DVA) with a vestibular implant, using the functional Head Impulse Test (fHIT). Methods: A 72-year-old female, with bilateral vestibulopathy and fitted with...

Dizziness, slow visual tracking, or blurred vision following active head (or body) movements are among the most common symptoms reported following sport-related concussion, often related to concurrent dysfunctions of the vestibular system. In some cases, symptoms persist even if bedside and auxiliary standard vestibular tests are unremarkable. New...

Introduction: Bilateral vestibulopathy (BV) is a chronic condition in which vestibular function is severely impaired or absent on both ears. Oscillopsia is one of the main symptoms of BV. Oscillopsia can be quantified objectively by functional vestibular tests, and subjectively by questionnaires. Recently, a new technique for testing functionally e...

Dynamic visual acuity (DVA) provides an overall functional measure of visual stabilization performance that depends on the vestibulo-ocular reflex (VOR), but also on other processes, including catch-up saccades and likely visual motion processing. Capturing the efficiency of gaze stabilization against head movement as a whole, it is potentially val...

Objectives: The video head impulse test (vHIT) provides as output a gain value that summarizes the behavior of the vestibulo-ocular reflex as the ratio of a measure of eye movement to the corresponding measure of head movement and is not directly informative of the functional effectiveness of the motor response. The functional HIT (fHIT) is based...

Cerebellar impairment may cause deficits in horizontal gaze holding, leading to centrifugal gaze-evoked nystagmus during fixation of eccentric targets. Healthy individuals show a weak drift leading to physiological nystagmus only at large gaze angles. These drifts are due to imperfect memory of the neural circuitry generating the eye position signa...

Cerebellar impairment may cause deficits in horizontal gaze holding, leading to centrifugal gaze-evoked nystagmus during fixation of eccentric targets. Healthy individuals show a weak drift leading to physiological nystagmus only at large gaze angles. These drifts are due to imperfect memory of the neural circuitry generating the eye position signa...

The description of a biological system using a mathematical model is the most effective means to specify the functioning of a quantitative hypothesis, providing at the same time the ability to make predictions that can be further tested experimentally. The Vestibulo-Ocular Reflex (VOR), and more generally the ocular motor control system has been on...

Saccades are the rapid eye movements that we continuously make to shift gaze from one object of interest to another. These voluntary eye movements not only are exemplary to describe various forms of ocular motor and cognitive function but also have a fundamental role as a prototype for understanding general principles in motor neurosciences. Their...

The functional head impulse test is a new test of vestibular function based on the ability to recognize the orientation of a Landolt C optotype that briefly appears on a computer screen during passive head impulses imposed by the examiner over a range of head accelerations. Here, we compare its results with those of the video head impulse test on a...

Objective To investigate cerebellar dysfunctions and quantitatively characterize specific oculomotor changes in ataxia-telangiectasia-like disorder (ATLD), a rare autosomal recessive disease caused by mutations in the MRE11 gene. Additionally, to further elucidate the pathophysiology of cerebellar damage in the ataxia-telangiectasia (AT) spectrum d...

The 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 Burs...

Background: 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. Obj...

In response to passive high-acceleration head impulses patients with low vestibulo-ocular reflex (VOR) gains often produce covert (executed while the head is still moving) corrective saccades in the direction of deficient slow phases. Here we examined 23 patients using passive, and nine also active, head impulses with acute (< 10 days from onset) u...

Key points: The cerebellum is the core structure controlling gaze stability. Chronic cerebellar diseases and acute alcohol intoxication affect cerebellar function, inducing, among others, gaze instability as gaze-evoked nystagmus. Gaze-evoked nystagmus is characterized by increased centripetal eye-drift. It is used as an important diagnostic sign...

The increasing number of applications of silver nanoparticles (AgNP) prompted us to assess their toxicity in vivo. We have investigated their effects on wild type and transgenic Caenorhabditis elegans (C. elegans) strains expressing two prototypic amyloidogenic proteins: β2-microglobulin and Aβ peptide3–42. The use of C. elegans allowed us to highl...

Introduction Patients with bilateral vestibular dysfunction cannot fully compensate passive head rotations with eye movements, and therefore experience oscillopsia, making everyday activities, such as walking or driving harder to undertake. Their dynamic vision during passive head movements depends on their residual vestibulo-ocular reflex (VOR) fu...

Postural control during quiet standing is evaluated by analyzing CoP sway, easily measured using a force platform. However, recent proliferation of motion tracking systems made easily available an estimate of the CoM location. Traditional CoP-based measures presented in literature provide information about age-related changes in postural stability...

The head impulse test (HIT) is nowadays recognized as the gold standard for clinical testing of the angular vestibulo-ocular reflex (VOR). By imposing unpredictable, abrupt head rotations in canal pairs' planes it aims at unveiling the dysfunction of the semicircular canal towards which the head is rotated based on Ewald's II law. Functional testin...

Patients with bilateral vestibular dysfunction cannot fully compensate passive head rotations with eye movements, and experience disturbing oscillopsia. To compensate for the deficient vestibulo-ocular reflex (VOR), they have to rely on re-fixation saccades. Some can trigger "covert" saccades while the head still moves; others only initiate saccade...

The problem of a correct fall risk assessment is becoming more and more critical with the ageing of the population. In spite of the available approaches allowing a quantitative analysis of the human movement control system's performance, the clinical assessment and diagnostic approach to fall risk assessment still relies mostly on non-quantitative...

Monitoring balance and movement has proven useful in many applications ranging from fall risk assessment, to quantifying exercise, studying people habits and monitoring the elderly. Here we present a versatile, wearable instrument capable of providing objective measurements of limb movements for the assessment of motor and balance control abilities...

The aims of this study were to develop and evaluate reliability of a quantitative assessment tool for upper limb sense of position on the horizontal plane. We evaluated 15 healthy individuals (controls) and 9 stroke patients. A robotic device passively moved one arm of the blindfolded participant who had to actively move his/her opposite hand to th...

We present a new electronic insole for wireless monitoring of motor activities and shoe comfort. The proposed device, equipped with both ZigBee transmission and local data storage allows unobtrusive, long term monitoring of subjects outside the laboratory, during natural behavior activites, such as daily living and sports. The system detailed in th...

Brain-Computer Interfaces (BCI) aim at translating brain signals, typically ElectroEncephaloGraphy (EEG), into commands for external devices. Spatial filters are powerful tools for EEG classification, able to reduce spatial blurring effects. In particular, optimal spatial filters have been designed to classify EEG signals based on band power featur...

Introduction: Patients affected by bilateral vestibulopathy are unable to stabilize gaze during head movements and experience disturbing oscillopsia. This affects everyday activities. To compensate for their impaired vestibulo-ocular reflex (VOR), they have to trigger re-fixation saccades: some can perform short-latency saccades (“covert”) during h...

Objectives/hypothesis: The possibility that long-term mobile phone use increases the incidence of astrocytoma, glioma and acoustic neuroma has been investigated in several studies. Recently, our group showed that direct exposure (in a surgical setting) to cell phone electromagnetic fields (EMFs) induces deterioration of auditory evoked cochlear ne...

BCI systems aim at developing man-machine communication channels independent of the intervention of muscles. This is accomplished by recognizing specific mental states and using their detection to trigger actions in a computer controlled environment. Brain activity is acquired, typically through EEG, and is then processed in order to compute featur...

We 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. W...

The main goal of a BCI system is to create a communication channel independent of muscles' activation. This is accomplished by recognizing specific mental states and using their detection to trigger actions in a computer controlled environment. To achieve such goal it is necessary to record brain activity, typically through EEG, and then process th...

Peripheral 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 d...

BACKGROUND: The rotational vestibulo-ocular reflex (rVOR) generates compensatory eye movements in response to rotational head accelerations. The velocity-storage mechanism (VSM), which is controlled by the vestibulo-cerebellar nodulus and uvula, determines the rVOR time constant. In healthy subjects, it has been suggested that self-motion perceptio...

We 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 ran...

In clinical settings, static ocular torsion is assessed by taking a fundus photograph and measuring the angle between a horizontal line and the line connecting the fovea to the head of the optic nerve (centro-cecal axis rotation; CCAR). We developed and tested a system specifically aimed at CCAR measurements, based on low-cost commercial hardware,...

Movement analysis is a powerful tool for the diagnosis of neurological conditions, as well as patient assessment and follow-up during rehabilitation programs. In spite of the available systems allowing a quantitative analysis of a subject's movement control performances, the clinical assessment and diagnostic approach still relies mostly on non-qua...

IntroductionAdaptive NetworksNeural NetworksLearningStructural AdaptationNeuro-Fuzzy NetworksGenetic Algorithms

This chapter discusses the translational vestibulo-ocular reflex (tVOR) is a complex reflex that accounts for target position in space both in terms of the distance to the target and its eccentricity, and for the direction of motion. Study of the reflex during pure translation indicates that the reflex considers all these factors in determining the...

The rapid spread of devices generating electromagnetic fields (EMF) has raised concerns as to the possible effects of this technology on humans. The auditory system is the neural organ most frequently and directly exposed to electromagnetic activity owing to the daily use of mobile phones. In recent publications, a possible correlation between mobi...

Self-motion perception after a sudden stop from a sustained rotation in darkness lasts approximately as long as reflexive eye movements. We hypothesized that, after an angular velocity step, self-motion perception and reflexive eye movements are driven by the same vestibular pathways. In 16 healthy subjects (25-71 years of age), perceived rotationa...

Rapid shifts of the point of visual fixation between equidistant targets require equal-sized saccades of each eye. The brainstem medial longitudinal fasciculus (MLF) plays a cardinal role in ensuring that horizontal saccades between equidistant targets are tightly yoked. Lesions of the MLF--internuclear ophthalmoparesis (INO)--cause horizontal sacc...

The vestibulo-ocular reflex (VOR) uses head angular acceleration information transduced by the semicircular canals in the inner ear in order to drive eye movements that compensate for head rotations, and thus stabilize the visual scene on the retina. Peripheral and central vestibular pathologies may impair the function of the VOR, so that compensat...

The study of postural sway during quiet stance has proved to be a useful approach to investigate the function of the balance system. Recent studies have suggested that providing information on postural sway to vestibular patients through biofeedback may improve their balance awareness and therefore reduce their risk of falling. One drawback common...

Transcranial magnetic stimulation (TMS) transiently induces an electrical field in the tissues beneath the area of application, thereby perturbing local cortical activity if applied over the scalp. It can therefore be used to modulate cerebellar function in healthy humans. Even though the role of the cerebellum in eye movement control and adaptatio...

The study of postural sway during quiet stance has proved a useful approach to investigate the function of the balance system. Recent studies have suggested that providing information on postural sway to vestibular patients through various biofeedback devices may improve their balance awareness and therefore reduce their risk of falling. One drawba...

The vestibulo-ocular reflex (VOR) uses head angular acceleration information transduced by the semicircular canals in the inner ear in order to drive eye movements that compensate for head rotations, and thus stabilize the visual scene on the retina. Peripheral and central vestibular pathologies may impair the function of the VOR so that compensati...

The slow phase velocity of the rVOR response to a step of constant velocity head rotation is best represented by a model with two time constants. Two main models, based on different physiological hypotheses, have been proposed in the literature. Although their structures and their parameters are different, these two models have often been considere...

Single-unit recordings of vestibular afferents from the semicircular canals of squirrel monkeys have shown that the cupular time constant (T(c)) is between 5 and 6 sec. Such recordings obviously cannot be performed in humans, and the corresponding values have thus been inferred to be somewhat longer based on their size and on the cupula-endolymph s...

Saccadic oscillations threaten clear vision by causing image motion on the retina. They are either purely horizontal (ocular flutter) or multidimensional (opsoclonus). We propose that ion channel dysfunction in the burst cell membrane is the underlying abnormality. We have tested this hypothesis by simulating a neuromimetic computational model of t...

Essential tremor (ET) is the most common movement disorder and its pathophysiology is unknown. We hypothesize that increased membrane excitability in motor circuits has a key role in the pathogenesis of ET. Specifically, we propose that neural circuits controlling ballistic movements are inherently unstable due to their underlying reciprocal innerv...

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