Analyzing the dynamics of hand tremor time series

We investigate physiological, essential and parkinsonian hand tremor measured by the acceleration of the streched hand. Methods from the theory of dynamical systems and from stochastics are used. It turns out that the physiological tremor can be described as a linear stochastic process, and that the parkinsonian tremor is nonlinear and deterministic, even chaotic. The essential tremor adopts a middle position, it is nonlinear and stochastic.     

Frequency and displacement amplitude relations for normal hand tremor.

Spectral analysis of hand tremor records obtained from normal subjects during continuous extension of the hand for 15-45 min revealed that the root-mean-square (rms) displacement amplitude of the tremor increased from control levels of about 30 mum to levels on the order of 100-1,000 times control. Associated with this increase in the displacement was a systematic decrease in the hand tremor frequency from control values of 8-9 Hz to values of 4-6 Hz. Spectral analysis of demodulated extensor EMG records indicated a consistent relation between EMG modulation amplitude at the tremor frequency and the tremor displacement amplitude for tremor records with rms displacement above about 100 mum. No consistent relation was found between these two variables for tremor records with displacements below 100 mum. Consideration of both mechanical and neural reflex effects indicated that a viscoelastic-mass mechanism primarily determined the small-amplitude (less than 100 mum) tremors, while the large displacement tremors may have involved both mechanical and neural feed back factors.     

Pathological tremors as diffusional processes

 Two types of pathological tremors, essential and Parkinsonian, are studied using dynamical systems theory. It is shown that pathological tremors can be characterized as diffusional processes. The time-scale range for the diffusional scaling law to be valid starts from about one to several tens of the mean oscillation period. This time-scale range contrasts sharply with the predictable time scale for deterministic chaos, which is usually only a small fraction of the mean oscillation period. The diffusions in pathological tremors are usually anomalous. A number of quantities are designed to characterize the diffusions in the tremor. Their relevance to potential clinical applications is discussed. It is argued that in order to discriminate between Parkinsonian and essential tremors, quantities not of purely dynamical origin may be more useful, since purely dynamical quantities emphasize more the dynamical similarities between the two types of tremors. Received: 30 May 2001 / Accepted in revised form: 6 November 2001     

Energy and fractal characteristics of physiological and pathological tremors of the human hand

Tremors (involuntary shaking) were compared in healthy subjects and patients with the tremulous form of Parkinsonism sustaining isometric effort of the hand. For this purpose, fractal analysis and multilevel wavelet decomposition of tremor were used, and the energy characteristics determined on the basis of the spectral density of the energy of detailed components obtained at different levels of decomposition. The calculated fractal and energy characteristics of the tremor of healthy subjects were significantly lower than those of patients. If the patients took antiparkinsonian drugs at their usual doses, the characteristics shifted towards normal values. The decrease in the fractal dimension indicates an increase in the strength of the correlation in the dynamics of involuntary shaking. Thus, the characteristics studied allow not only physiological and pathological tremors to be discriminated, but also the strategy of selection of optimal drugs for relieving Parkinsonian tremor to be developed.     

Dependence of peripheral tremor on mechanical perturbations: a modeling study

The present study scrutinizes the popular view that tremors of central origin but not those of peripheral origin are largely resistant to mechanical perturbations. We explore the effects of perturbations in a well-established model of peripheral tremor and document that (a) tremor frequency can remain unchanged when spring or weight loads are added, (b) entrainment by external drives can be limited to drives of similar frequency, and (c) resetting of tremor phase by torque pulses can remain fractional. This resistance to mechanical perturbations arises in the model because peripheral neuromuscular dynamics act as a limit-cycle oscillator which, by its very nature, will absorb moderate changes to signals and parameters. We conclude from our study that resistance to mechanical perturbations is not an exclusive property of central tremors, but rather may also be found in peripheral tremors. Other criteria are therefore needed to distinguish between different origins of tremor. Received: 8 April 1998 / Accepted in revised form: 6 October 1998     

Clinicians’ Tendencies to Under-Rate Parkinsonian Tremors in the Less Affected Hand

The standard assessment method for tremor severity in Parkinson’s disease is visual observation by neurologists using clinical rating scales. This is, therefore, a subjective rating that is dependent on clinical expertise. The objective of this study was to report clinicians’ tendencies to under-rate Parkinsonian tremors in the less affected hand. This was observed through objective tremor measurement with accelerometers. Tremor amplitudes were measured objectively using tri-axis-accelerometers for both hands simultaneously in 53 patients with Parkinson’s disease during resting and postural tremors. The videotaped tremor was rated by neurologists using clinical rating scales. The tremor measured by accelerometer was compared with clinical ratings. Neurologists tended to under-rate the less affected hand in resting tremor when the contralateral hand had severe tremor in Session I. The participating neurologists corrected this tendency in Session II after being informed of it. The under-rating tendency was then repeated by other uninformed neurologists in Session III. Kappa statistics showed high inter-rater agreements and high agreements between estimated scores derived from the accelerometer signals and the mean Clinical Tremor Rating Scale evaluated in every session. Therefore, clinicians need to be aware of this under-rating tendency in visual inspection of the less affected hand in order to make accurate tremor severity assessments.     

Features of parkinsonian and essential tremor of the human hand

Using spectral, wavelet, multifractal, and recurrence analyses we examined the features of involuntary shaking (tremor) that occur during the performance of a given motor task. The task was to maintain the efforts of fingers under isometric conditions by a healthy subject, a patient with primary bilateral parkinsonism, and a patient with essential tremor syndrome. The physiological tremor was characterized by the lowest amplitude, a broad power spectrum, the lowest energy of the wavelet spectrum, the highest degree of multifractality, the lowest degree of determinism, and the highest entropy of the recurrence time density. In the case of the essential tremor we observed a significant enhancement of the wavelet spectrum energy and a decrease of the oscillation complexity. This was evident via the occurrence of clear peaks in the power spectra, a decrease in the degree of multifractality, the emergence of a quasi-periodic structure in the recurrence diagrams, an increase in determinism and a decrease of the entropy of recurrence time density. All these trends were increased for the parkinsonian tremor data. These characteristics enable us to quantitatively estimate the degree of deviation of motor function from the healthy case.     

Tremor modulation in patients with Parkinson’s disease compared to healthy counterparts during loaded postural holding

Through examining tremor dynamics, the study sought to investigate the effects of load characteristics upon control strategies in patients with Parkinson’s disease (PD) during postural holding. Eleven untreated patients and eleven healthy adults conducted a static pointing task with an outstretched arm, with a manipulated load of 100 g on the index finger. Oscillatory activities in the upper limb were contrasted between the unloaded and loaded conditions. The results showed that PD patients demonstrated abnormal modulation of tremor amplitude in the finger, hand, and upper arm in the opposing load condition. When the load was applied, the PD patients presented a nearly opposite pattern of tremor coupling between limb segments, contrary to the normal release and enhancement of tremor coupling in the finger–hand and hand–forearm complexes, respectively. Principal component analysis suggested that normal postural tremors could be explained by a load-dependent component that had high communality with tremors of the distal segments. In contrast, major principal components of PD tremor were invariant to load addition. Multi-segment tremors in PD were atypically organized during loaded postural holding, signifying that coordinative control of the upper limb in the patients was impaired in the absence of exploitation of a germane distal strategy against inertial perturbation.     

What happened to VIM thalamotomy for Parkinson's disease?

A prospective review of 75 of 190 parkinsonian patients undergoing unilateral thalamotomy was displayed with a computer graphics technique examining three equal consecutive groups from the pre-, early, and late L-dopa eras. Histograms for average function and scattergrams of individual patient's performance preoperatively and up to 2 years postoperatively were prepared. No ipsilateral effects or consistent iatrogenic deterioration of any function were identified. 2 years after surgery, 82% had no tremor in the contralateral fingers or hand and 7% had almost no tremor; contralateral tremor elsewhere was infrequent. Rigidity and manual dexterity improved less strikingly, the latter only reflecting abolition of tremor; locomotion, speech, facial movement and handwriting did not improve. There was no mortality, but 8% had persistent significant complications. VIM thalamotomy remains the treatment of choice for severe drug-resistant parkinsonian tremor.     

Cross-correlation analysis of thalamic neurons and EMG activity in parkinsonian tremor

Bursting activity in cells cross-correlated with electromyographic (EMG) activity during parkinsonian tremor. Statistically significant evidence of cross-correlation was found for 49% of cells located at the lesion target for relief of tremor. Statistically significant correlation was found for 90% of cells having tremor frequency power greater than twice 'average power' at nontremor frequencies. This population of cells may be involved in the generation of parkinsonian tremor.     

Failure of Arm Movement Control in Stroke Patients,Characterized by Loss of Complexity

We study the mechanism of human arm-posture control by means of nonlinear dynamics and quantitative time series analysis methods. Utilizing linear and nonlinear measures in combination, we find that pathological tremors emerge in patient dynamics and serve as a main feature discriminating between normal and patient groups. The deterministic structure accompanied with loss of complexity inherent in the tremor dynamics is also revealed. To probe the underlying mechanism of the arm-posture dynamics, we further analyze the coupling patterns between joints and components, and discuss their roles in breaking of the organization structure. As a result, we elucidate the mechanisms in the arm-posture dynamics of normal subjects responding to the gravitational force and for the reduction of the dynamic degrees of freedom in the patient dynamics. This study provides an integrated framework for the origin of the loss of complexity in the dynamics of patients as well as the coupling structure in the arm-posture dynamics.     

Physiological and pathological oscillatory networks in the human motor system.

Human brain functions are heavily contingent on neural interactions both at the single neuron and the neural population or system level. Accumulating evidence from neurophysiological studies strongly suggests that coupling of oscillatory neural activity provides an important mechanism to establish neural interactions. With the availability of whole-head magnetoencephalography (MEG) macroscopic oscillatory activity can be measured non-invasively from the human brain with high temporal and spatial resolution. To localise, quantify and map oscillatory activity and interactions onto individual brain anatomy we have developed the 'dynamic imaging of coherent sources' (DICS) method which allows to identify and analyse cerebral oscillatory networks from MEG recordings. Using this approach we have characterized physiological and pathological oscillatory networks in the human sensorimotor system. Coherent 8 Hz oscillations emerge from a cerebello-thalamo-premotor-motor cortical network and exert an 8 Hz oscillatory drive on the spinal motor neurons which can be observed as a physiological tremulousness of the movement termed movement discontinuities. This network represents the neurophysiological substrate of a discrete mode of motor control. In parkinsonian resting tremor we have identified an extensive cerebral network consisting of primary motor and lateral premotor cortex, supplementary motor cortex, thalamus/basal ganglia, posterior parietal cortex and secondary somatosensory cortex, which are entrained in the tremor or twice the tremor rhythm. This low frequency entrapment of motor areas likely plays an important role in the pathophysiology of parkinsonian motor symptoms. Finally, studies on patients with postural tremor in hepatic encephalopathy revealed that this type of tremor results from a pathologically slow thalamocortical and cortico-muscular coupling during isometric hold tasks. In conclusion, the analysis of oscillatory cerebral networks provides new insights into physiological mechanisms of motor control and pathophysiological mechanisms of tremor disorders.     

Organization of physiological tremors and coordination solutions to postural pointing on an uneven stance surface

The study investigated the destabilization effect on multi-segment physiological tremors and coordinative control for a postural-suprapostural task under different stance conditions. Twenty volunteers executed postural pointing from a level surface and a seesaw balance board; meanwhile, physiological tremors of the whole postural system and fluctuation movements of fingertip/stance surface were recorded. In reference to level stance, seesaw stance led to much fewer tremor increments of the upper limb and less fluctuation movement of the fingertip than tremor increment of the lower limb and rolling movement of the stance surface. Tremor coupling between the adjacent segments organized differentially with stance surface. In reference to level stance, seesaw stance reinforced tremor coupling of the upper limb but enfeebled the coupling in the arm-lumbar and calf-foot complexes. Stance-related differences in physiological tremors could be explained by characteristic changes in the primary and secondary principal components (PC1 and PC2), with relatively high communality with segment tremors of the lower and upper limbs, respectively. Seesaw stance introduced a prominent 4-8Hz spectral peak in PC1 and potentiated 1-4Hz and 8-12Hz spectral peaks of PC2. Structural reorganization of physiological tremors with stance configuration suggests that seesaw stance involves distinct suprapostural and postural synergies for regulating degree of freedom in joint space.     

A method for the objective determination of tremors in the rat]

Two methods for determining tremors in the rat, acceleration pick-up and electromyogram, including electronic evaluation by impluse rate and frequency are described technically, and the results obtained with either method are compared. Both methods allow quantitative analysis of the drug induced (arecoline) tremor. Electromyographically, the tremor effect can be recorded already after lower doses compared with the electro-mechanical method. Besides, the EMG can be employed on immobilized animals.     

Carpal Tunnel Syndrome in Patients with Tremor Dominant Parkinson’s Disease

Background

Unilateral hand tremor is one of the cardinal symptoms of Parkinson’s disease. Additionally, mechanical traumatic hand movement is one of the risk factors for carpal tunnel syndrome. Our objective in this study was to examine whether repetitive mechanical movement may be related to the development of carpal tunnel syndrome in Parkinson’s disease with unilateral hand tremor using neurophysiological methods.

Methods

The study participants included 33 de novo Parkinson’s disease patients with unilateral hand tremor, and we compared the tremor hand and non-tremor hand within the same patients.

Results

Seven (21.2%) of the 33 patients had carpal tunnel syndrome. All of carpal tunnel syndrome patients showed neurophysiological abnormalities in both the hand without tremor and the hand with tremor. In addition, in patients without carpal tunnel syndrome, the sensory nerve action potential was lower in the hand without tremor than in the hand with tremor, although there were no significant differences.

Conclusions

We concluded that hand tremor in de novo Parkinson’s disease patients was not directly related to the development of carpal tunnel syndrome. In contrast, more frequent use of hand without tremor may induce mechanical loading and may be associated with CTS in the hand without tremor. Early diagnosis of Parkinson’s disease and proper education in hand use may be essential for preventing carpal tunnel syndrome in Parkinson’s disease tremor patients.     

Selection of the optimal lesion site for the relief of parkinsonian tremor on the basis of spectral analysis of neuronal firing patterns

Techniques for quantitatively describing the firing properties of neurons have been used to identify thalamic cells with a firing pattern which is correlated with EMG activity during tremor. By locating these cells relative to the anterior border of the somatosensory nucleus and the anterior commissure-posterior commissure line, it may be possible to select the optimal lesion site for the relief of parkinsonian tremor on a rational rather than an empirical basis.     

Nonlinear mechanical property of tracheal cartilage: a theoretical and experimental study

BACKGROUND: Despite being the stiffest airway of the bronchial tree, the trachea undergoes significant deformation due to intrathoracic pressure during breathing. The mechanical properties of the trachea affect the flow in the airway and may contribute to the biological function of the lung. METHOD: A Fung-type strain energy density function was used to investigate the nonlinear mechanical behavior of tracheal cartilage. A bending test on pig tracheal cartilage was performed and a mathematical model for analyzing the deformation of tracheal cartilage was developed. The constants included in the strain energy density function were determined by fitting the experimental data. RESULT: The experimental data show that tracheal cartilage is a nonlinear material displaying higher strength in compression than in tension. When the compression forces varied from -0.02 to -0.03N and from -0.03 to -0.04N, the deformation ratios were 11.03+/-2.18% and 7.27+/-1.59%, respectively. Both were much smaller than the deformation ratios (20.01+/-4.49%) under tension forces of 0.02 to 0.01N. The Fung-type strain energy density function can capture this nonlinear behavior very well, whilst the linear stress-strain relation cannot. It underestimates the stability of trachea by exaggerating the displacement in compression. This study may improve our understanding of the nonlinear behavior of tracheal cartilage and it may be useful for the future study on tracheal collapse behavior under physiological and pathological conditions.     

Neostriatal muscarinic receptor subtypes involved in the generation of tremulous jaw movements in rodents implications for cholinergic involvement in parkinsonism

Several studies have shown that a number of pharmacological and neurochemical conditions in rats can induce jaw movements that are described as "vacuous" or "tremulous". For several years, there has been some debate about the clinical significance of various drug-induced oral motor syndromes. Nevertheless, considerable evidence now indicates that the non-directed, chewing-like movements induced by cholinomimetics have many of the characteristics of parkinsonian tremor. These movements are characterized largely by vertical deflections of the jaw, which occur in the same 3-7 Hz peak frequency that is typical of parkinsonian tremor. Cholinomimetic-induced tremulous jaw movements are suppressed by a number of different antiparkinsonian drugs, including scopolamine, benztropine, L-DOPA, apomorphine, bromocriptine, ropinirole, pergolide, amantadine, diphenhydramine and clozapine. A combination of anatomical and pharmacological research in rats has implicated M4 receptors in the ventrolateral neostriatum in the generation of tremulous jaw movements. Mice also show cholinomimetic-induced jaw movements, and M4 receptor knockout mice demonstrate subtantially reduced levels of jaw movement activity, as well as increased locomotion. Taken together, these data are consistent with the hypothesis that a centrally-acting M4 antagonist may be useful as a treatment for parkinsonian symptoms, including tremor.     

Load dependence of simulated central tremor

Previous studies have argued that tremors of central versus peripheral origin can be distinguished based on their load dependence: the frequency of peripheral tremor decreases when a weight is added to the tremulous limb, while the frequency of central tremors remains unchanged. The present study scrutinizes the latter statement. We simulated central tremor using a simple network of coupled neural oscillators, which receives proprioceptive feedback from the motor periphery. The network produced a self-sustained, stable oscillation. When the gain of proprioceptive feedback was high, oscillation frequency decreased in the presence of an inertial load. When the gain was low, the oscillation frequency was load independent. We conclude that load dependence is not an exclusive property of peripheral tremors but may be found in tremors of central origin as well. Therefore, the load test is not sufficient to reject a central tremor origin. Received: 1 October 1998 / Accepted in revised form: 28 January 1999     

Significance of the potential role of pharmacological MRI (phMRI) in diagnosis of Parkinson’s disease

The initial diagnosis of Parkinson's disease (PD) is currently based on a clinical assessment.Many patients who receive an initial diagnosis of PD have parkinsonian features related to other diseases s...