Tremor Suppression Research Articles

Closed-Loop Deep Brain Stimulation for Essential Tremor Based on Thalamic Local Field Potentials.

BackgroundHigh‐frequency thalamic stimulation is an effective therapy for essential tremor, which mainly affects voluntary movements and/or sustained postures. However, continuous stimulation may deliver unnecessary current to the brain due to the intermittent nature of the tremor.ObjectiveWe proposed to close the loop of thalamic stimulation by detecting tremor‐provoking movement states using local field potentials recorded from the same electrodes implanted for stimulation, so that the stimulation is only delivered when necessary.MethodsEight patients with essential tremor participated in this study. Patient‐specific support vector machine classifiers were first trained using data recorded while the patient performed tremor‐provoking movements. Then, the trained models were applied in real‐time to detect these movements and triggered the delivery of stimulation.ResultsUsing the proposed method, stimulation was switched on for 80.37 ± 7.06% of the time when tremor‐evoking movements were present. In comparison, the stimulation was switched on for 12.71 ± 7.06% of the time when the patients were at rest and tremor‐free. Compared with continuous stimulation, a similar amount of tremor suppression was achieved while only delivering 36.62 ± 13.49% of the energy used in continuous stimulation.ConclusionsThe results suggest that responsive thalamic stimulation for essential tremor based on tremor‐provoking movement detection can be achieved without any requirement for external sensors or additional electrocorticography strips. Further research is required to investigate whether the decoding model is stable across time and generalizable to the variety of activities patients may engage with in everyday life. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society

Non-invasive suppression of essential tremor via phase-locked disruption of its temporal coherence

Aberrant neural oscillations hallmark numerous brain disorders. Here, we first report a method to track the phase of neural oscillations in real-time via endpoint-corrected Hilbert transform (ecHT) that mitigates the characteristic Gibbs distortion. We then used ecHT to show that the aberrant neural oscillation that hallmarks essential tremor (ET) syndrome, the most common adult movement disorder, can be transiently suppressed via transcranial electrical stimulation of the cerebellum phase-locked to the tremor. The tremor suppression is sustained shortly after the end of the stimulation and can be phenomenologically predicted. Finally, we use feature-based statistical-learning and neurophysiological-modelling to show that the suppression of ET is mechanistically attributed to a disruption of the temporal coherence of the aberrant oscillations in the olivocerebellar loop, thus establishing its causal role. The suppression of aberrant neural oscillation via phase-locked driven disruption of temporal coherence may in the future represent a powerful neuromodulatory strategy to treat brain disorders.

Innovative and affordable wearable solution for suppression of hand tremors

Hand tremor influences a huge number of individuals around the world. Tremor is characterised as unintended, cadenced muscle development. Albeit most tremors neither reason serious medical issues nor threaten life, most patients experience many troubles in performing everyday exercises. It is humiliating to numerous individuals, particularly more seasoned people. Tremor negatively affects personal satisfaction and decreases the ability to perform everyday life undertakings such as eating, drinking, writing, and changing clothing. Some patients with mild tremor do not visit doctors if tremor does not hinder their daily life activities. Their situations often worsen over time. There is currently very few to almost no external solution existing to cope with this medical condition. We have developed a glove that is able to dynamically conceive the motion of a user's hand and ascertain the difference between intentional movement and unintentional movement. Further, we have quantified, verified and attempted to provide a haptic response to the users' fingers with the help of coin motors to help counteract the unwanted vibration.

A Layer Jamming Soft Glove for Hand Tremor Suppression

Tremors are a common movement disorder that affects a person's life adversely. With various drawbacks of current treatment methods, there is a need for a mechanical solution. The authors present a soft orthosis based on layer jamming for the suppression of hand tremors. A vacuum supplied to the layer jamming elements which contain a stack of layers attached to the glove leads to increased stiffness in the glove, suppressing the tremor. The behavior of the tremor in a cohort of patients in Sri Lanka was studied and showed that the tremor's mean frequency was 5.05 ± 2.03 Hz. An existing analytical model was modified and verified experimentally to select the layer jamming element. An element with sandpaper (320 grade) and tracing paper was chosen based on the high stiffness provided at a lower weight (total weight of the glove = 30g). Experimental results show minimal variation in stiffness for vacuum pressures between 10-50 kPa (abs.). The performance evaluation on a test rig was used to verify the efficacy of the glove and showed optimal placement on the palmar side with a mean tremor amplitude reduction of 78.32%. Clinical trials conducted on 11 recruited tremor patients showed a mean frequency power reduction of 41.74 ± 12.11%, 41.99 ± 14.82%, and 24.71 ± 12.18% in the index and middle fingers and in grasping, respectively with a maximum power reduction of 59.15%. The soft, low weight orthosis shows a high tremor suppression in both the test rig and clinical experiments.

Innovative and affordable wearable solution for suppression of hand tremors

Innovative and affordable wearable solution for suppression of hand tremors

Real-Time Voluntary Motion Prediction and Parkinson's Tremor Reduction Using Deep Neural Networks.

Wearable tremor suppression devices (WTSD) have been considered as a viable solution to manage parkinsonian tremor. WTSDs showed their ability to improve the quality of life of individuals suffering from parkinsonian tremor, by helping them to perform activities of daily living (ADL). Since parkinsonian tremor has been shown to be nonstationary, nonlinear, and stochastic in nature, the performance of the tremor models used by WTSDs is affected by their inability to adapt to the nonlinear behaviour of tremor. Another drawback that the models have is their limitation to estimate or predict one step ahead, which introduces delay when used in real time with WTSDs, which compromises performance. To address these issues, this work proposes a deep neural network model that learns the correlations and nonlinearities of tremor and voluntary motion, and is capable of multi-step prediction with minimal delay. A generalized model that is task and user-independent is presented. The model achieved an average estimation percentage accuracy of 99.2%. The average future voluntary motion prediction percentage accuracy with 10, 20, 50, and 100 steps ahead was 97.0%, 94.0%, 91.6%, and 89.9%, respectively, with prediction time as low as 1.5 ms for 100 steps ahead. The proposed model also achieved an average of 93.8% ± 1.5% in tremor reduction when it was tested in an experimental setup in real time. The tremor reduction showed an improvement of 25% over the Weighted Fourier Linear Combiner (WFLC), an estimator commonly used with WTSDs.

An Improved Modeling of Parkinson’s Tremor and Investigation of Some Approaches to Remove this Symptom

In this research, an improved model of Parkinsonian tremor is presented by using a mathematical and computational approach. In Parkinson’s disease (PD), an abnormal signal is produced by basal ganglia (BG). This signal goes to the thalamus, then enters cortex and after interaction with peripheral system goes to muscle and finally appears as tremor. In the presented model, all of the mentioned process are simulated. Also, the skeletal muscle model as well as the central nervous system (basal ganglia, thalamus, cortex and supplementary motor area) and peripheral nervous system (spinal reflex) mechanisms are considered. In addition, two methods for tremor suppression are applied in this paper, 1) deep brain stimulation (DBS) which affects dopamine level in BG and 2) a mechanical method which is based on a negative feedback. The accuracy and efficiency of the presented simulation are demonstrated by comparison of the obtained results with those obtained by clinical tests.

Increased structural connectivity of thalamic stimulation sites to motor cortex relates to tremor suppression

Deep brain stimulation (DBS) of the ventral intermediate nucleus (VIM-DBS) is a highly successful treatment for medication-refractory essential tremor (ET). Clinical outcomes are dependent on accurate targeting. Here, we aim to develop a framework for connectivity-guided DBS targeting by evaluating probabilistic tractography and clinical response at both initial programming (IP) and clinical follow-up (CF).Magnetic resonance imaging and clinical outcomes were evaluated in 23 ET patients who were treated by VIM-DBS at the University of California Los Angeles (20 at IP, 18 at CF, 14 at both). Lead-DBS was used to model the volume of tissue activated tissue (VTA) based on programming configurations at both IP and CF. Probabilistic tractography, calculated in FSL, was used to evaluate 1) clinically weighted whole brain connectivity of VTA; 2) connectivity between VTA and freesurfer-derived target regions of interest (ROI) including primary motor, premotor, and prefrontal cortices, and cerebellum; and 3) volume of intersection between VTA and probabilistic tractography-based segmentation of the thalamus. At IP, individual contacts were scored as high or low efficacy based on acute tremor improvement. At CF, clinical response was measured by percent of change of the Clinical Rating Scale for Tremor (CRST) compared to preoperative scores. Contributions from each target ROI to clinical response was measured using logistic regression for IP and linear regression for CF.The clinically weighted map of whole brain connectivity of VTA shows preferential connectivity to precentral gyrus and brainstem/cerebellum. The volume of intersection between VTA and thalamic segmentation map based on probabilistic connectivity to primary motor cortex was a significant predictor of contact efficacy at IP (OR = 2.26 per 100 mm3 of overlap, p = .04) and percent change in CRST at CF (β = 14.67 per 100 mm3 of overlap, p = .003).Targeting DBS to the area of thalamus most connected to primary motor cortex based on probabilistic tractography is associated with superior outcomes, providing a potential guide not only for lead targeting but also therapeutic programming.

Towards wearable tremor suppression using dielectric elastomer stack actuators

Active wearable tremor suppression devices apply actuators to the human body to produce joint torques that reduce tremor motion. This potential alternative to medications and surgery has the advantage of providing robust tremor treatment that is non-invasive, but the bulkiness of typical engineering actuators currently prohibits clinical implementations. Dielectric elastomer stack actuators (DESAs) offer a potential pathway towards achieving soft, low-profile tremor suppression devices: DESAs have similar mechanical properties as human muscles and can conform to the human limb. However, low actuation levels and a lack of commercial availability limit the development of DESA-based orthoses. Employing a control approach that only suppresses tremor while allowing the actuators to follow voluntary motion passively significantly decreases actuation requirements to improve potential for clinical devices. Still, DESAs that may offer the necessary actuation characteristics require specialized equipment and techniques. This research advances DESA-based tremor suppression by experimentally demonstrating DESA-based suppression of tremor-like signals on a scaled system using easily manufactured DESAs. Further discussion quantifies the DESA parameters that will enable physical implementations of human-scale tremor suppression and identifies pathways towards achieving those parameters.

Thalamic Deep Brain Stimulation in Essential Tremor Plus Is as Effective as in Essential Tremor.

The new essential tremor (ET) classification defined ET-plus (ET-p) as an ET subgroup with additional neurological signs besides action tremor. While deep brain stimulation (DBS) is effective in ET, there are no studies specifically addressing DBS effects in ET-p. 44 patients with medication-refractory ET and thalamic/subthalamic DBS implanted at our center were postoperatively classified into ET and ET-p according to preoperative documentation. Tremor suppression with DBS (stimulation ON vs. preoperative baseline and vs. stimulation OFF), measured via the Fahn–Tolosa–Marin tremor rating scale (TRS), stimulation parameters, and the location of active contacts were compared between patients classified as ET and ET-p. TRS scores at baseline were higher in ET-p. ET-p patients showed comparable tremor reduction as patients with ET, albeit higher stimulation parameters were needed in ET-p. Active electrode contacts were located more dorsally in ET-p of uncertain reason. Our data show that DBS is similarly effective in ET-p compared to ET. TRS scores were higher in ET-p preoperatively, and higher stimulation parameters were needed for tremor reduction compared to ET. The latter may be related to a more dorsal location of active electrode contacts in the ET-p group of this cohort. Prospective studies are warranted to investigate DBS in ET-p further.

Chronic embedded cortico-thalamic closed-loop deep brain stimulation for the treatment of essential tremor.

Deep brain stimulation (DBS) is an approved therapy for the treatment of medically refractory and severe movement disorders. However, most existing neurostimulators can only apply continuous stimulation [open-loop DBS (OL-DBS)], ignoring patient behavior and environmental factors, which consequently leads to an inefficient therapy, thus limiting the therapeutic window. Here, we established the feasibility of a self-adjusting therapeutic DBS [closed-loop DBS (CL-DBS)], fully embedded in a chronic investigational neurostimulator (Activa PC + S), for three patients affected by essential tremor (ET) enrolled in a longitudinal (6 months) within-subject crossover protocol (DBS OFF, OL-DBS, and CL-DBS). Most patients with ET experience involuntary limb tremor during goal-directed movements, but not during rest. Hence, the proposed CL-DBS paradigm explored the efficacy of modulating the stimulation amplitude based on patient-specific motor behavior, suppressing the pathological tremor on-demand based on a cortical electrode detecting upper limb motor activity. Here, we demonstrated how the proposed stimulation paradigm was able to achieve clinical efficacy and tremor suppression comparable with OL-DBS in a range of movements (cup reaching, proximal and distal posture, water pouring, and writing) while having a consistent reduction in energy delivery. The proposed paradigm is an important step toward a behaviorally modulated fully embedded DBS system, capable of delivering stimulation only when needed, and potentially mitigating pitfalls of OL-DBS, such as DBS-induced side effects and premature device replacement.

Design of fiber-reinforced soft bending pneumatic artificial muscles for wearable tremor suppression devices

Soft robotics is a rapidly evolving field offering novel solutions in the development of wearable technologies. Soft pneumatic artificial muscles in particular, have seen widespread use in the development of human scale rehabilitative and assistive wearables. However, these soft actuators have not yet been adapted to address the complex dynamic regime of active (essential tremor) and resting (Parkinson’s disease) hand tremor, the most common movement disorder affecting humans. Current solutions to address hand tremor involve expensive medication and surgical interventions, as well as wearable assistive devices that fall short of providing an effective compact design for the suppression of hand tremor. This study focuses on the design of a novel lightweight, compact, bending actuator that will be capable of actively suppressing hand tremor when adapted into an assistive wearable device. The proposed fiber-reinforced bending pneumatic artificial muscle (BPAM), including its design specifications, fabrication process, theoretical modeling, and experimental characterization, are detailed. The developed actuator was capable of producing sinusoidal trajectories with peak-to-peak amplitudes of 40° and a bandwidth of 8 Hz, the dynamic regime of pathological hand tremor. The ability of the fiber-reinforced BPAM to act within the dynamic regime of hand tremor demonstrates its potential to be further developed into a system capable of the active suppression of hand tremor.

Quantitative Evidence of Pathological Tremor Suppression after Functional Electrical Stimulation.

The article's abstract is not available.

Analytical and experimental studies on particle damper used for tremor suppression

Tremor is an involuntary movement that makes many patients suffer, and passive absorbers used in wearable robot are proved to be effective for tremor suppression. A particle damper is a kind of a passive vibration control device taking advantage of energy dissipation and momentum exchange caused by particle collisions. To apply particle damping technology in reducing tremor amplitude in the human hand, this study establishes a mechanical model of the particle damper for tremor suppression and obtains its steady-state solutions under simplified tremor excitation. The accuracy of steady-state solutions and the particle damper effectiveness in reducing tremor is validated by numerical simulations and experimental studies. To further explore its damping mechanism, some important damper parameters are then analyzed. It is shown that increasing the particle mass leads to an increase of the particle damper performance for tremor suppression, but it has an upper limit. The provided damping of the particle damper becomes approximately independent of the tremor frequency and the tremor amplitude within a certain range, which indicates that a particle damper with reasonable design is suitable for tremor suppression.

Fully implanted adaptive deep brain stimulation in freely moving essential tremor patients

Objective. Deep brain stimulation (DBS) is a safe and established treatment for essential tremor (ET) and several other movement disorders. One approach to improving DBS therapy is adaptive DBS (aDBS), in which stimulation parameters are modulated in real time based on biofeedback from either external or implanted sensors. Previously tested systems have fallen short of translational applicability due to the requirement for patients to continuously wear the necessary sensors or processing devices, as well as privacy and security concerns. Approach. We designed and implemented a translation-ready training data collection system for fully implanted aDBS. Two patients chronically implanted with electrocorticography strips over the hand portion of M1 and DBS probes in the ipsilateral ventral intermediate nucleus of the thalamus for treatment of ET were recruited for this study. Training was conducted using a translation-ready distributed training procedure, allowing a substantially higher degree of control over data collection than previous works. A linear classifier was trained using this system, biased towards activating stimulation in accordance with clinical considerations. Main results. The clinically relevant average false negative rate, defined as fraction of time during which stimulation dropped below clinical levels during movement epochs, was 0.036. Tremor suppression, calculated through analysis of gyroscope data, was 33.2% more effective on average with aDBS than with continuous DBS. During a period of free movement with aDBS, one patient reported a slight paresthesia; patients noticed no difference in treatment efficacy between systems. Significance. Here is presented the first translation-ready training procedure for a fully embedded aDBS control system for MDs and one of the first examples of such a system in ET, adding to the consensus that fully implanted aDBS systems are sufficiently mature for broader deployment in treatment of movement disorders.

Active vibration control in human forearm model using paired piezoelectric sensor and actuator

An active vibration control system to monitor and suppress the human forearm tremor is proposed in this article. The forearm is modelled as a uniform flexible continuous beam supported by a pin joint and a rotational spring at one end, whereas the other end is free. The beam is covered with a layer of piezoelectric sensor on its top surface and a layer of piezoelectric actuator on its bottom surface to form a control system, through which a closed-loop active control paradigm is implemented for tremor suppression. The governing equation of motion is derived using the Hamilton principle as well as the Galerkin procedure, leading to a second-order ordinary differential equation in time. The vibration response of the structure to an external harmonic excitation, analogous to tremor, is obtained analytically, enabling parametric study of the control system for tremor reduction. Using the obtained analytical expression, the effects of various parameters such as the control gain, the piezoelectric coefficient and the dielectric constant on the vibration response are studied. The results indicated that the proposed active vibration control system is an effective tool for active vibration control. Increasing the control gain of the control system as well as the magnitude of the piezoelectric constant decreased the amplitude of vibration, whereas the dielectric constant of the piezoelectric material did not show to have a significant effect on the beam vibration. The obtained results will pave the way for further experimental exploration to take and fabricate the most appropriate piezoelectric material and to design an effective active vibration control system for tremor suppression in people with Parkinson’s disease.

Multibody Analysis and Control of a Full-Wrist Exoskeleton for Tremor Alleviation.

Uncontrollable shaking in the human wrist, caused by pathological tremor, can significantly undermine the power and accuracy in object manipulation. In this paper, the design of a tremor alleviating wrist exoskeleton (TAWE) is introduced. Unlike the works in the literature that only consider the flexion/extension (FE) motion, in this paper, we model the wrist joint as a constrained three-dimensional (3D) rotational joint accounting for the coupled FE and radial/ulnar deviation (RUD) motions. Hence TAWE, which features a six degrees-of-freedom (DOF) rigid linkage structure, aims to accurately monitor, suppress tremors, and provide light-power augmentation in both FE and RUD wrist motions. The presented study focuses on providing a fundamental understanding of the feasibility of TAWE through theoretical analyses. The analytical multibody modeling of the forearm-TAWE assembly provides insight into the necessary conditions for control, which indicates that reliable control conditions in the desired workspace can be acquired by tuning the design parameters. Nonlinear regressions are then implemented to identify the information that is crucial to the controller design from the unknown wrist kinematics. The proposed analytical model is validated numerically with V-REP and the result shows good agreement. Simulations also demonstrate the reliable performance of TAWE under controllers designed for tremor suppression and movement assistance.

Comparing Programming Sessions of Vim-DBS.

Background: Essential Tremor (ET) is a progressive neurological disorder characterized by postural and kinetic tremor most commonly affecting the hands and arms. Medically intractable ET can be treated by deep brain stimulation (DBS) of the ventral intermediate nucleus of thalamus (VIM). We investigated whether the location of the effective contact (most tremor suppression with at least side effects) in VIM-DBS for ET changes over time, indicating a distinct mechanism of loss of efficacy that goes beyond progression of tremor severity, or a mere reduction of DBS efficacy.Methods: We performed programming sessions in 10 patients who underwent bilateral vim-DBS surgery between 2009 and 2017 at our department. In addition to the intraoperative (T1) and first clinical programming session (T2) a third programming session (T3) was performed to assess the effect- and side effect threshold (minimum voltage at which a tremor suppression or side effects occurred). Additionally, we compared the choice of the effective contact between T1 and T2 which might be affected by a surgical induced “brain shift.”Discussion: Over a time span of about 4 years VIM-DBS in ET showed continuous efficacy in tremor suppression during stim-ON compared to stim-OFF. Compared to immediate postoperative programming sessions in ET-patients with DBS, long-term evaluation showed no relevant change in the choice of contact with respect to side effects and efficacy. In the majority of the cases the active contact at T2 did not correspond to the most effective intraoperative stimulation site T1, which might be explained by a brain-shift due to cerebral spinal fluid loss after neurosurgical procedure.

Distribution of tremor among the major degrees of freedom of the upper limb in subjects with Essential Tremor

ObjectiveAlthough Essential Tremor is one of the most common movement disorders, we do not currently know which muscles are most responsible for tremor. Determining this requires multiple steps, one of which is characterizing the distribution of tremor among the degrees of freedom (DOF) of the upper limb. MethodsUpper-limb motion was recorded while 22 subjects with ET performed postural and kinetic tasks involving a variety of limb configurations. We calculated the mean distribution of tremor among the seven DOF from the shoulder to the wrist, as well as the effect of limb configuration, repetition, and subject characteristics (sex, tremor onset, duration, and severity) on the distribution. ResultsOn average, kinetic tremor was greatest in forearm pronation-supination and wrist flexion–extension, intermediate in shoulder internal-external rotation and wrist radial-ulnar deviation and then shoulder flexion–extension and elbow flexion–extension, and least in shoulder abduction–adduction. The average distribution of postural tremor was similar except for forearm pronation-supination, which played a smaller role than in kinetic tremor. Limb configuration and subject characteristics did significantly affect tremor, but practically only in forearm pronation-supination and wrist flexion–extension. There were no significant differences between repetitions, indicating that the distribution was consistent over the duration of the experiment. ConclusionsThis paper presents a thorough characterization of tremor distribution from the shoulder to the wrist. SignificanceUnderstanding which DOF exhibit the most tremor may lead to more targeted peripheral tremor suppression.

A Soft Exoskeleton for Tremor Suppression Equipped with Flexible Semiactive Actuator.

Pathological tremor is a kind of movement disorder that affects a wide range of patients with Parkinson's disease and essential tremor. Different from available clinical treatments for tremor, including drug and surgery therapy, a novel soft exoskeleton for tremor suppression (SETS) based on assistive technologies is proposed in this study. The SETS system is equipped with a controllable flexible semiactive actuator based on magnetorheological fluid. To overcome the drawbacks of traditional fluidic semiactive actuators, we devise a soft semiactive actuator that is a combination of cylinder-piston damper and elastic fluidic damper. The overall system is characterized with low mass, compact structure, comfortable wearability as well as real-time adjustability for tremor attenuation with varying intensity. The SETS can assist in suppressing tremor of wrist joint in three degrees of freedom. The prototype weighs about 255 g and can yield a maximum damping force of about 11 N. Simulation studies and experimental tests were carried out to evaluate the performance of the system. The results show that the SETS could reduce wrist tremor regarding magnitude of acceleration and angular velocity by 61.39% and 56.22%, respectively, which validate the manifest mechanical efficiency of this functional system.