Tremor Amplitude Research Articles

The Cerebral Network of Parkinson's Tremor: An Effective Connectivity fMRI Study.

Parkinson's resting tremor has been linked to pathophysiological changes both in the basal ganglia and in a cerebello-thalamo-cortical motor loop, but the role of those circuits in initiating and maintaining tremor remains unclear. Here, we test whether and how the cerebello-thalamo-cortical loop is driven into a tremor-related state by virtue of its connectivity with the basal ganglia. An internal replication design on two independent cohorts of tremor-dominant Parkinson patients sampled brain activity and tremor with concurrent EMG-fMRI. Using dynamic causal modeling, we tested: (1) whether activity at the onset of tremor episodes drives tremulous network activity through the basal ganglia or the cerebello-thalamo-cortical loop and (2) whether the basal ganglia influence the cerebello-thalamo-cortical loop through connectivity with the cerebellum or motor cortex. We compared five physiologically plausible circuits, model families in which transient activity at the onset of tremor episodes (assessed using EMG) drove network activity through the internal globus pallidus (GPi), external globus pallidus, motor cortex, thalamus, or cerebellum. In each family, we compared two models in which the basal ganglia and cerebello-thalamo-cortical loop were connected through the cerebellum or motor cortex. In both cohorts, cerebral activity associated with changes in tremor amplitude (using peripheral EMG measures as a proxy for tremor-related neuronal activity) drove network activity through the GPi, which effectively influenced the cerebello-thalamo-cortical loop through the motor cortex. We conclude that cerebral activity related to Parkinson's tremor first arises in the GPi and is then propagated to the cerebello-thalamo-cortical circuit. Parkinson's resting tremor has been linked to pathophysiological changes both in the basal ganglia and in a cerebello-thalamo-cortical motor loop, but the role of those circuits in initiating and maintaining tremor remains unclear. Using dynamic causal modeling of concurrently collected EMG-fMRI data in two cohorts of Parkinson's patients, we showed that cerebral activity associated with changes in tremor amplitude drives network activity through the basal ganglia. Furthermore, the basal ganglia effectively influenced the cerebello-thalamo-cortical circuit through the motor cortex (but not the cerebellum). Out findings suggest that Parkinson's tremor-related activity first arises in the basal ganglia and is then propagated to the cerebello-thalamo-cortical circuit.

Tremor Amplitude is Greater in the Mediolateral Direction than Vertical During Handgun Aiming Tasks.

PURPOSE: In aiming at a target, humans produce small involuntary fluctuations in the aiming limb which may hamper performance. While often studied in the vertical axis, these fluctuations occur in all axes. The current study compared vertical and mediolateral tremor amplitude during different handgun aiming postures. METHODS: Thirty volunteers stood 21 feet from a target and aimed a weighted mock handgun for 10 sec with an accelerometer affixed to each wrist and the gun barrel. Participants performed five trials per condition. Amplitude (RMS) of the acceleration signals were computed. Two hand grip (bilateral, unilateral), two arm positions (bent, straight), and two segments (forearm, gun) were analyzed in conjunction with the two directions (VT, ML). RESULTS: Across all conditions tremor amplitude in the mediolateral direction was significantly greater than the vertical direction (VT: .017+.006g vs. ML: 0.021+.005g, p<.001). Additionally significant interaction effects were seen for direction by hand grip (p<.001) as well as direction by arm position (p=.002). For hand grip, vertical tremor was significantly lower than mediolateral and bilateral tremor was significantly lower than unilateral. For arm position, vertical tremor was significantly lower than mediolateral and bent arm tremor was significantly lower than straight arm. There were no significant interaction effects for direction by segment (p=.173). CONCLUSION: Across numerous hand gun aiming postures mediolateral tremor amplitude was consistently higher than the vertical tremor amplitude. This may be due to the neurological and mechanical factors of the limb, the limbs resistance to gravity, or the effort of control. Further research is needed to examine the interaction of mediolateral and vertical tremor.

Fatiguing a Single Limb leads to Bilateral Changes in Postural Tremor and Forearm Muscle Activity

For healthy adults, the physiological tremor within a single limb segment is uncorrelated to that in the contralateral limb. However, it has been suggested that some bilateral relation for tremor does exist, but that this would only emerge under conditions where the neuromuscular system is perturbed such as during unilateral fatigue. PURPOSE: To assess the effect of externally loading the index finger on bilateral tremor dynamics and forearm muscle activity. METHODS: Eighteen young adults participated in the study (mean age 22.4+4.2 yrs.). For all tasks, bilateral hand and finger tremor and forearm surface EMG activity (extensor digitorum) were collected. Subjects were seated with both forearms resting on a flat surface and their hands and index fingers extended (unsupported). Three 30 s trials were collected under this condition. For the fatigue conditions, a 400 gram weight was suspended from the index finger of one limb. Subjects were required to hold both fingers in an extended (horizontal) position with the weight attached for two, 2-min trials (rests were given between trials). The fatigue protocol was then repeated for the opposite limb. RESULTS: As expected, fatiguing a single limb led to significant increases in tremor amplitude (pre-fatigue: 0.18+0.04 ms-2; post: 0.37+0.08 ms-2, p<0.02), extensor muscle activity (pre: 0.11+0.04 mV; Post: 0.24+0.06 mV, p<0.05). In addition, fatiguing a single limb led to changes in the contralateral (un-weighted) limb, significant increases in the amount of muscle activity (pre: 0.10+0.03 mV; Post: 0.17+0.03 mV, p<0.05) and the amplitude of finger tremor (pre: 0.16+0.05 ms-2; post: 0.27+0.04 ms-2, p<0.05). However, these contralateral effects were observed even though there was no evidence of inter-limb coupling of tremor (r’s=0.08-0.18, p=0.64). CONCLUSION: Overall, the results demonstrated that the effects of fatiguing a single, distal limb segment are not restricted to that effector unit. Loading the index finger of one limb led to bilateral increases in both tremor amplitude and related forearm muscle activity. However, these changes were present even though there was no evidence of any tremor coupling between limbs. The findings illustrate that these bilateral effects may be mediated by an overflow effect caused by increased neural drive to the exercising limb.

Development of method for quantifying essential tremor using a small optical device

BackgroundClinical assessment scales are the most common means used by physicians to assess tremor severity. Some scientific tools that may be able to replace these scales to objectively assess the severity, such as accelerometers, digital tablets, electromyography (EMG) measurement devices, and motion capture cameras, are currently available. However, most of the operational modes of these tools are relatively complex or are only able to capture part of the clinical information; furthermore, using these tools is sometimes time consuming. Currently, there is no tool available for automatically quantifying tremor severity in clinical environments. New methodWe aimed to develop a rapid, objective, and quantitative system for measuring the severity of finger tremor using a small portable optical device (Leap Motion). ResultsA single test took 15s to conduct, and three algorithms were proposed to quantify the severity of finger tremor. The system was tested with four patients diagnosed with essential tremor. Comparison with existing methodThe proposed algorithms were able to quantify different characteristics of tremor in clinical environments, and could be used as references for future clinical assessments. ConclusionsA portable, easy-to-use, small-sized, and noncontact device (Leap Motion) was used to clinically detect and record finger movement, and three algorithms were proposed to describe tremor amplitudes.

본태성 진전 환자의 진전특성에 대한 수행과제 및 부위의 영향

Abstract: Essential tremor is a neurological disorder with a tremor of the arms and hands. It is well known thatessential tremor is characterized by the postural tremor and the action tremor. There has been no report on the quan-titative difference in the characteristics of two tremor types. The purpose of this study was to investigate the possibledifference in tremor characteristics of postural and action tremors. Seventeen patients with essential tremor (68.9± 7.9years, 7 men, 10 women) participated in this study. Patients performed the tasks of postural maintenance (armsoutstretched) and daily actions (spiral drawing). Three-axes (pitch, roll and yaw) gyro sensors were attached on indexfinger, back of hand and forearm, from which the segment and the joint angular velocities were calculated. Outcomemeasure was the tremor amplitude defined as the root-mean-square mean of the vector-sum angular velocity at seg-ments and joints. Two-way ANOVA showed that task and joint had main factor on the tremor amplitude (p 0.05). However, tremor amplitude at the wrist joint differed among the tasks (p < 0.05), and it was greater inthe action tasks than in postural task. Tremor was greater at finger segments than at hand and forearm and itincreased in action tasks. The results of this study would be helpful for the understanding and task-specific treat-ments of the essential tremor.Key words: essential tremor, task specific, angular velocity, action tremor, postural tremor

Tremor during ice-stream stick slip

Abstract. During the 200 km-scale stick slip of the Whillans Ice Plain (WIP), West Antarctica, seismic tremor episodes occur at the ice–bed interface. We interpret these tremor episodes as swarms of small repeating earthquakes. The earthquakes are evenly spaced in time, and this even spacing gives rise to spectral peaks at integer multiples of the recurrence frequency ∼ 10–20 Hz. We conduct numerical simulations of the tremor episodes that include the balance of forces acting on the fault, the evolution of rate- and state-dependent fault friction, and wave propagation from the fault patch to a seismometer located on the ice. The ice slides as an elastic block loaded by the push of the upstream ice, and so the simulated basal fault patch experiences a loading velocity equal to the velocity observed by GPS receivers on the surface of the WIP. By matching synthetic seismograms to observed seismograms, we infer fault patch area ∼ 10 m2, bed shear modulus ∼ 20 MPa, effective pressure ∼ 10 kPa, and frictional state evolution distance ∼ 1 μm. Large-scale slip events often occur twice daily, although skipped events have been increasing in frequency over the last decade. The amplitude of tremor (recorded by seismometers on the ice surface) is greater during the double wait time events that follow skipped events. The physical mechanism responsible for these elevated amplitudes may provide a window into near-future subglacial conditions and the processes that occur during ice-stream stagnation.

Tremor pattern differentiates drug-induced resting tremor from Parkinson disease

ObjectiveDAT-SPECT, is a well-established procedure for distinguishing drug-induced parkinsonism from Parkinson's disease (PD). We investigated the usefulness of blink reflex recovery cycle (BRrc) and of electromyographic parameters of resting tremor for the differentiation of patients with drug-induced parkinsonism with resting tremor (rDIP) from those with resting tremor due to PD. MethodsThis was a cross-sectional study. In 16 patients with rDIP and 18 patients with PD we analysed electrophysiological parameters (amplitude, duration, burst and pattern) of resting tremor. BRrc at interstimulus intervals (ISI) of 100, 150, 200, 300, 400, 500 and 750 msec was also analysed in patients with rDIP, patients with PD and healthy controls. All patients and controls underwent DAT-SPECT. ResultsRest tremor amplitude was higher in PD patients than in rDIP patients (p < 0.001), while frequency and burst duration were higher in rDIP than in PD (p < 0.001, p < 0.003, respectively). Resting tremor showed a synchronous pattern in all patients with rDIP, whereas it had an alternating pattern in all PD patients (p < 0.001). DAT-SPECT was normal in rDIP patients while it was markedly abnormal in patients with PD. ConclusionsIn the absence of DAT-SPECT, the pattern of resting tremor can be considered a useful investigation for differentiating rDIP from PD.

Method for Real-Time Evaluation of Discharge Rate of Volcanic Ash – Case Study on Intermittent Eruptions at the Sakurajima Volcano, Japan –

A method for evaluating the volcanic ash discharge rate by using seismic and ground deformation signals is proposed to obtain this rate in real time for southern Kyushu’s Sakurajima volcano. This volcano repeats vulcanian eruptions accompanying significant ground deformation showing deflation and nonvulcanian type eruptions that emit the minor emissions of volcanic ash associated with volcanic tremors but without significant ground deformation. We examined ground deformation and seismic amplitude as they relate to monthly sums of volcanic ash weight ejected from craters. We found that in monthly sums, both deflation ground deformation and the amplitude of volcanic tremors correlate positively with the weight of ejected volcanic ash. A linear combination of terms for ground deformation, seismic amplitude and a correction factor correlates better than single parameter of deflation or seismic amplitude with volcanic ash weight. The linear combination provides the volcanic ash discharge rate in quasi-real time and the total amount of volcanic ash distributed over a wide area immediately after a volcanic eruption ends.

A STUDY OF EFFICACY OF TREATMENT FOR ESSENTIAL TREMOR USING TREMOROGRAPHY

Background: Essential tremor is one of the most prevalent extrapyramidal disorders, while treatment efficacy in such patients remains low. Clinical polymorphism of essential tremor requires a differentiated treatment approach, that should be implemented with consideration of objective tremor parameters. Aim: To study efficacy of treatment of essential tremor based on tremorography. Materials and methods: We followed up 85 patients with essential tremor (mean age, 69.05±1.2 years) who were treated with anticonvulsants as monotherapy (primidone or topiramate), or with combination treatment with non-selective beta-blockers (propranolol), anxiolytics (hydroxizine, etifoxine) and aminophenylbutyric acid. During the treatment, we assessed changes in functional status by Fahn-Tolosa-Marin Tremor Severity Scale and by tremorography. Results: Under treatment with primidone, there was a decrease in global tremor assessment of postural tremor (p=0.036) and of action tremor (p=0.001). During treatment with topiramate, there was a decrease in global tremor assessment in all tests performed (p<0.0002). Non-specific treatment (anxiolytics) exerted a positive effect on the functional state of patients with essential tremor. Conclusion: Tremor amplitude and duration are the objective parameters that define its severity. The treatment guidelines for essential tremor in the elderly patients have been developed.

Triggered tectonic tremor in various types of fault systems of Japan following the 2012 Mw8.6 Sumatra earthquake

AbstractTectonic tremor, an extremely stress‐sensitive seismic phenomenon occurring in the brittle‐ductile transition section of a fault, is associated with the shearing mechanism of slow slip. Observations of triggered tremor can facilitate the evaluation of the existence of background ambient tremor and slow‐slip events. This paper presents widespread triggered tremor sources in Japan initiated by the surface waves of the 2012 Mw8.6 Sumatra earthquake on strike‐slip and thrust faults, in the deep volcanic low‐frequency earthquake active area, in the shallow tectonic tremor and very low frequency earthquake active regions, and in the subduction zone. In most regions, the amplitudes of triggered tremor are generally logarithmically proportional to the dynamic stress caused by various triggering earthquakes. Our observations suggest that triggered tremor in the newly discovered sources is the result of a more rapid rate of background ambient tremor, and evidence has suggested the existence of ambient tremor in some regions.

Commentary: Clinical Correlates of Raphe Serotonergic Dysfunction in Early Parkinson's Disease.

Growing and clinical evidence supports the conclusion that Parkinson’s Disease (PD) is a complex multisystem disorder not exclusively affecting the dopaminergic circuits. In fact, the dopaminergic neuronal loss does not cover all the clinical aspects of PD. Therefore, different non-dopaminergic neurotransmitter systems have been invoked as playing a role in the PD clinical picture. Principally, the inefficiency of serotonergic circuitry has been demonstrated in PD animal models, as well as in post-mortem and in vivo human studies. In the recent article published in Brain, Zahi Qamhawi and colleagues interrogated 123I-FP-CIT single-photon emission computed tomography documenting raphe serotonergic dysfunction in a large group of early PD patients compared to a subset of possible PD patients without evidence of dopaminergic deficit (SWEDD) and a population of healthy controls (1). This paper combined an accurate clinical evaluation with a sophisticated neuroimaging protocol and documented in PD patients a mean raphe serotonin (5-HT) transporter availability significantly lower than both SWEDD patients and controls. These findings, achieved in a large cohort of PD patients, enforced previous autoptic examinations documenting serotonergic neurons loss due to Lewy body pathology in the raphe nuclei of PD patients (2). Accordingly, neuroimaging studies have shown the progressive 5-HT transporter availability reduction in the raphe nuclei as PD pathology progresses (3–5). It is well accepted that concentration of 5-HT and its metabolite 5-hydroxyindolacetic acid (5-HIAA) in CSF reflects the serotonergic metabolism and turnover in the CNS (6, 7). We performed a case-control study investigating CSF levels of 5-HT and 5-HIAA in a cohort of PD patients, after a 3-day dopaminergic therapy withdrawal and in absence of serotonergic agents (8). We demonstrated the significant reduction of CSF 5-HT and 5-HIAA concentrations in PD patients compared to controls. We also found the significant reduction of CSF 5-HT and 5-HIAA in the PD population with respect to Alzheimer’s Disease patients (8), thus highlighting that the impairment of serotonergic system could represent a specific effect of synuclein-mediated neurodegeneration (8). As a matter of fact, novel experimental studies in alpha-synuclein (α-syn) mouse model of PD showed the impairment of serotonergic system owing to the intracellular accumulation of α-syn in serotonergic neurons coupled with the reduction of 5-HT levels in lower brainstem (9). Based on the clinical presentation, Qamhawi and collegues divided PD patients into two subgroups corresponding to patients with and without resting tremor. Remarkably, patients with tremor had lower mean raphe 5-HT transporter availability than patients unaffected by tremor. Since tremor amplitude, constancy, and severity negatively correlated with raphe 5-HT transporter availability in the whole PD cohort, authors suggested that the serotonergic system inefficiency could be responsible for parkinsonian tremor. This finding was consistent with previous studies detecting an association between 5-HT receptor availability in the raphe nuclei and severity of parkinsonian tremor (10). However, in our CSF study, we found no differences in CSF 5-HT and 5-HIAA levels between tremor dominant and non-tremor dominant patients. This discrepancy could be ascribed to the fact that Qamhawi and collegues studied de novo early PD patients, whereas we investigated patients with higher Hoehn and Yahr stage and greater motor disability at the Unified PD Rating Scale-motor section. It could be of interest to evaluate in follow-up studies how the serotonergic transmission damage may influence PD motor symptoms along with the progression of the disease. Concurrently, the reliability of the proposed difference in raphe 5-HT transporter availability found by Qamhawi and coworkers in early PD patients should be also analyzed in more advanced PD patients. Remarkably, Qamhawi and coauthors documented that raphe 5-HT transporter availability did not correlate with PD non-motor symptoms, such as fatigue, depression, and sleep-wake cycle disturbances. In agreement with this finding, we did not identify mutual interplays linking CSF 5-HT and 5-HIAA concentrations to depression, apathy, and sleep disturbances. Although our report sustained Qamhawi and coworkers results, literature proposes controversial data regarding the involvement of serotonergic pathways breakage in the pathophysiology of PD non-motor symptoms (11), thus requiring further investigations. All considering, we suppose that the reduced 5-HT transporter availability, as shown by Qamhawi and collegues, and the 5-HT synthesis, metabolism, and turnover impairment, resulting in reduced CSF levels of 5-HT and 5-HIAA (8) may both contribute to the serotonergic transmission dysfunction evident in PD. Hence, serotonin circuitry inefficiency could represent the fitting partner of the dopaminergic deficit in PD.

Contribution of inter-muscular synchronization in the modulation of tremor intensity in Parkinson's disease.

BackgroundInvoluntary central oscillations at single and double tremor frequencies drive the peripheral neuromechanical system of muscles and joints to cause tremor in Parkinson’s disease (PD). The central signal of double tremor frequency was found to correlate more directly to individual muscle EMGs (Timmermann et al. 2003). This study is aimed at investigating what central components of oscillation contribute to inter-muscular synchronization in a group of upper extremity muscles during tremor in PD patients.Methods11 idiopathic, tremor dominant PD subjects participated in this study. Joint kinematics during tremor in the upper extremity was recorded along with EMGs of six upper arm muscles using a novel experimental apparatus. The apparatus provided support for the upper extremity on a horizontal surface with reduced friction, so that resting tremor in the arm can be recorded with a MotionMonitor II system. In each subject, the frequencies of rhythmic firings in upper arm muscles were determined using spectral analysis. Paired and pool-averaged coherence analyses of EMGs for the group of muscles were performed to correlate the level of inter-muscular synchronization to tremor amplitudes at shoulder and elbow. The phase shift between synchronized antagonistic muscle pairs was calculated to aid coherence analysis in the muscle pool.ResultsRecorded EMG revealed that rhythmic firings were present in most recorded muscles, which were either synchronized to form phase-locked bursting cycles at a subject specific frequency, or unsynchronized with a random phase distribution. Paired coherence showed a stronger synchronization among a subset of recorded arm muscles at tremor frequency than that at double tremor frequency. Furthermore, the number of synchronized muscles in the arm was positively correlated to tremor amplitudes at elbow and shoulder. Pool-averaged coherence at tremor frequency also showed a better correlation with the amplitude of resting tremor than that of double tremor frequency, indicating that the neuromechanical coupling in peripheral neuromuscular system was stronger at tremor frequency.ConclusionsBoth paired and pool-averaged coherences are more consistent indexes to correlate to tremor intensity in a group of upper extremity muscles of PD patients. The central drive at tremor frequency contributes mainly to synchronize peripheral muscles in the modulation of tremor intensity.

Descent of tremor source locations before the 2014 phreatic eruption of Ontake volcano, Japan

On 27 September 2014, Ontake volcano, in central Japan, suddenly erupted without precursory activity. We estimated and tracked the source locations of volcanic tremor associated with the eruption at high temporal resolution, using a method based on the spatial distribution of tremor amplitudes. Although the tremor source locations were not well constrained in depth, their epicenters were well located beneath the erupted crater and the summit. Tremor sources were seen to descend approximately 2 km over a period of several minutes prior to the beginning of the eruption. Detailed analysis of the time series of tremor amplitudes suggests that this descent is a robust feature. Our finding may be an important constraint for modeling the 2014 eruption of Ontake volcano as well as for monitoring activities on this and other volcanoes.

Shallowly driven fluctuations in lava lake outgassing (gas pistoning), Kīlauea Volcano

Lava lakes provide ideal venues for directly observing and understanding the nature of outgassing in basaltic magmatic systems. Kīlauea Volcano's summit lava lake has persisted for several years, during which seismic and infrasonic tremor amplitudes have exhibited episodic behavior associated with a rise and fall of the lava surface (“gas pistoning”). Since 2010, the outgassing regime of the lake has been tied to the presence or absence of gas pistoning. During normal behavior (no gas pistoning), the lake is in a “spattering” regime, consisting of higher tremor amplitudes and gas emissions. In comparison, gas piston events are associated with an abrupt rise in lava level (up to 20 m), during which the lake enters a “non-spattering” regime with greatly decreased tremor and gas emissions. We study this episodic behavior using long-term multidisciplinary monitoring of the lake, including seismicity, infrasound, gas emission and geochemistry, and time-lapse camera observations. The non-spattering regime (i.e. rise phase of a gas piston cycle) reflects gas bubbles accumulating near the top of the lake, perhaps as a shallow foam, while spattering regimes represent more efficient decoupling of gas from the lake. We speculate that the gas pistoning might be controlled by time-varying porosity and/or permeability in the upper portions of the lava lake, which may modulate foam formation and collapse. Competing models for gas pistoning, such as deeply sourced gas slugs, or dynamic pressure balances, are not consistent with our observations. Unlike other lava lakes which have cyclic behavior that is thought to be controlled by deeply sourced processes, external to the lake itself, we show an example of lava lake fluctuations driven by cycles of activity at shallow depth and close to the lake's surface. These observations highlight the complex and unsteady nature of outgassing from basaltic magmatic systems.

Repetitive control of functional electrical stimulation for induced tremor suppression

Tremor is an involuntary, oscillating, debilitating movement which affects over 50% of people with Multiple Sclerosis. In this paper an advanced paradigm, combining linearising action and repetitive control (RC), is developed to suppress tremor using functional electrical stimulation (FES) applied to wrist extensors/flexors. This innovative biomechanical approach to tremor suppression embeds learning from experience, and its effectiveness is confirmed in tests performed with nine healthy adults who attended a single one-hour session. Using FES, pathological wrist tremors (2.5, 3 or 4 Hz) were induced via extensor digitorum and a validated mechanical wrist-rig was used to collect data. Results confirmed statistically significant reduction in pathological movement, measured by path-length wrist movement and single peak amplitude of tremor.

Tidal sensitivity of tectonic tremors in Nankai and Cascadia subduction zones

AbstractTectonic tremors in subduction zones, which result from slip at the deep plate interface, are known to exhibit a 12.4 h periodicity in their activity, due to tidal influence. Because tidal stress can be calculated quantitatively, the response of the plate interface can yield quantitative information about its frictional property. The relation between tremor rate and tidal stress is investigated, and an exponential relation is widely confirmed, as observed by previous studies. This study particularly focuses on spatial variations of tidal sensitivity, which are compared with spatial variations of tremor duration and amplitude. The sensitivity is quantitatively defined by the exponent of the exponential relation, which can be related to the parameter aσ, or (a − b)σ in the rate‐and‐state friction law, where σ is effective normal stress. On the shallower tremor zone, short‐duration and large‐amplitude tremors occur followed by more sensitive tremors. Meanwhile, deeper tremors with longer duration and smaller amplitude show lower sensitivity, although along‐strike variation also exists. Typical and maximum sensitivities estimated here imply values for aσ or (a − b)σ of about 3 and 1 kPa, respectively. These correlations are consistent with a model in which the plate interface consists of a velocity‐strengthening background with embedded velocity‐weakening regions. The frictional heterogeneity may be statistically characterized by cluster size and density of the velocity‐weakening regions and controls the overall slip behavior. The observed depth dependency of tremor duration, amplitude, and sensitivity implies that frictional heterogeneity is controlled by physical quantities varying with depth, such as temperature or fluid amount.

Effective Management of Upper Limb Parkinsonian Tremor by IncobotulinumtoxinA Injections Using Sensor-based Biomechanical Patterns

BackgroundFocal treatment of Parkinson’s disease tremor by botulinum toxin type A incobotulinumtoxinA (BoNT-A) injections has been inadequately investigated and at best provides modest relief with significant muscle weakness. Complexity of multi-joint tremulous movements results in non-individualized dosing regimens. This 38-week open-label study used kinematic technology to guide muscle selection and improve efficacy of incobotulinumtoxinA (BoNT-A) injections for Parkinson’s disease tremor.MethodsParticipants (n=28) attended study visits at weeks 0, 6, 16, 22, 32, and 38, and were injected with BoNT-A at weeks 0, 16, and 32. During each visit, clinical tremor scales, the Unified Parkinson’s Disease Rating Scale (UPDRS) and the Fahn–Tolosa–Marin (FTM), and kinematic assessments were conducted. Participants performed rest and postural scripted tasks with motion sensors placed over the wrist, elbow, and shoulder joints where tremor was quantified by angular root mean square (RMS) amplitude in multiple degrees of freedom at each joint. Injection parameters were determined using the clinician’s interpretation of which muscles would contribute to the upper limb tremor biomechanics analyzed kinematically.ResultsKinematic measures of tremor amplitude allowed detailed segmentation of tremor into directional components at each arm joint permitting a statistically significant decrease in mean UPDRS item 20 (rest tremor) at week 16 (p=0.006) and at week 32 (p=0.014), and in FTM tremor severity scores at week 6 (p=0.024). Ten participants perceived mild muscle weakness following the third treatment, which did not interfere with performing activities of daily living.DiscussionKinematics is a simple method for standardizing assessments and treatment of upper limb Parkinson’s disease tremor, thereby personalizing tremor therapy and optimizing the effect of BoNT-A injections for Parkinson’s disease tremor.

Correlates Between Force and Postural Tremor in Older Individuals with Essential Tremor.

Essential tremor (ET) is commonly associated with kinetic tremor. However, other forms of tremor, such as force and postural tremor, may occur in ET with less severity. This study objectively assessed force and postural tremor characteristics in ET with the purpose of identifying the relationships between these tremors. Ten individuals with ET (age 71 ± 5years) and ten healthy controls (age 70 ± 5years) participated in the study. Force tremor was quantified as fluctuations in index finger abduction force during isometric contractions at 10% maximum voluntary contraction (MVC) and 60% MVC. Postural tremor was quantified as index finger acceleration when the subjects held their entire arm unsupported, and when their arm was supported so that only the index finger could move. Time- and frequency-domain parameters were extracted from tremor data, and then correlations within, and between, tremor subtypes were examined. ET force tremor was dependent on contraction intensity whereas postural tremor was unaffected by the level of limb support. Significant correlations existed between frequency components of postural tremor and force tremor amplitude. Force tremor amplitude normalised to the level of contraction intensity correlated to the proportion of power for postural tremor. These correlations were observed for both contraction intensities and both levels of postural support. The proportion of power represents the output of central oscillators in ET patients and therefore correlated well to force tremor. Given that significant relationships existed between spectral features of postural tremor and the overall force tremor amplitude, it is clear that these tremor modalities are not completely independent in older adults with ET.

Quantitative Assessment of Parkinsonian Tremor Based on an Inertial Measurement Unit

Quantitative assessment of parkinsonian tremor based on inertial sensors can provide reliable feedback on the effect of medication. In this regard, the features of parkinsonian tremor and its unique properties such as motor fluctuations and dyskinesia are taken into account. Least-square-estimation models are used to assess the severities of rest, postural, and action tremors. In addition, a time-frequency signal analysis algorithm for tremor state detection was also included in the tremor assessment method. This inertial sensor-based method was verified through comparison with an electromagnetic motion tracking system. Seven Parkinson’s disease (PD) patients were tested using this tremor assessment system. The measured tremor amplitudes correlated well with the judgments of a neurologist (r = 0.98). The systematic analysis of sensor-based tremor quantification and the corresponding experiments could be of great help in monitoring the severity of parkinsonian tremor.

The Clinical Evaluation of Parkinson's Tremor.

Parkinson’s disease harbours many different tremors that differ in distribution, frequency, and context in which they occur. A good clinical tremor assessment is important for weighing up possible differential diagnoses of Parkinson’s disease, but also to measure the severity of the tremor as a basis for further tailored treatment. This can be challenging, because Parkinson’s tremor amplitude is typically very variable and context-dependent. Here, we outline how we investigate Parkinson’s tremor in the clinic. We describe a simple set of clinical tasks that can be used to constrain tremor variability (cognitive and motor co-activation, several specific limb postures). This may help to adequately characterize the tremor(s) occurring in a patient with Parkinson’s disease.