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At least 487 records · Page 27Linked to original sources
PubMed2004

Postural tremor in Wilson's disease: a magnetoencephalographic study.

The following study included 5 Wilson's disease (WD) patients showing a right-sided postural forearm tremor (4-6 Hz) and addressed the question of whether the primary motor cortex (M1) is involved in tremor generation. Using a 122-channel whole-head neuromagnetometer and surface electromyogram (EMG), we investigated cerebromuscular coupling. Postural tremor was observed in a sustained 45-degree posture of the right-sided forearm. Data were analyzed using dynamic imaging of coherent sources (DICS), revealing cerebromuscular coupling between EMG and cerebral activity. Coherent sources were superimposed on individual high-resolution T1-weighted magnetic resonance images (MRI). Phase lags between EMG and cerebral areas showing strongest coherence were determined by means of a Hilbert transform of both signals. In all patients, postural tremor was associated with strong coherence between tremor EMG and activity in contralateral primary sensorimotor cortex (S1/M1) at tremor or double tremor frequency. Phase lag values between S1/M1 activity and EMG revealed efferent and afferent components in the corticomuscular coupling. Taken together, our results indicate that postural tremor in WD is mediated through a pathological oscillatory drive from the primary motor cortex.

Adult↗
PubMed2006

New actigraph for long-term tremor recording.

A new method of movement analysis is validated, allowing an actigraph to discriminate tremor from other movements and store duration and intensity measures of both movement types. For algorithm optimization, wrist acceleration was recorded in nine controls and nine Parkinson's disease patients, while simultaneously rating their observed tremor minute by minute on item 20 of the Unified Parkinson's Disease Rating Scale. An optimization procedure to minimize false positives in controls while maximizing tremor detection in patients resulted in false positive tremor classification in 2.4% +/- 2.5% of the movement time of control subjects (range, 0%-7%), while providing tremor classification in 82.1% +/- 15.4% of the movement time in patients (range, 55%-100%), correlating r = 0.93 with their averaged observed tremor score. A second, generalizability study showed that application of the optimized algorithm resulted in accurate classification of 71% +/- 14% of the observed tremor time (range, 46%-90%) in another 9 patients and in a false positive classification in only 0.5% +/- 0.8% of the time in another 10 controls (range, 0%-2.4%). The commercial availability of this actigraph now for the first time makes it possible to investigate tremor fluctuations over several weeks. An example is given of how long-term monitoring can be of use in evaluation of symptom management.

Aged↗
PubMed2006

Effect of rivastigmine on tremor in patients with Parkinson's disease and dementia.

The purpose of this study was to assess whether rivastigmine, a cholinergic agent, affects tremor features when given to improve cognition in demented Parkinson's disease (PD) patients. Demented PD patients (n = 26; Mini-Mental State Examination score, 13-25; age, 75.2 +/- 4.9 yr) were given rivastigmine (mean dose, 8.0 mg/day) for 12 weeks. They underwent tremor assessment before and during treatment. Global Tremor Score (GTS) was based on eight items specific to tremor in the Unified Parkinson's Disease Rating Scale. Tremor amplitude was also measured using accelerometers during the ON state in both hands in 19 patients. Drug therapy for other PD symptoms was unchanged. The mean group baseline GTS was 1.2 +/- 1.6 points, increasing to 1.6 +/- 2.4 points after treatment (mean increase, 0.4 +/- 1.2 points; P > 0.05). The GTS increased by 3.2 +/- 1.9 points (range, 1-5) in 7 patients (26.9%) and decreased by 1 +/- 0 points in 3 patients (11.5%). Accelerometric assessment showed a significant increase of the average tremor amplitude in the right hand (0.08 +/- 0.03 xg at baseline; 0.12 +/- 0.02 xg at Week 12 of treatment, P = 0.02). Left-hand tremor amplitude did not change. Rivastigmine caused only slight worsening of tremor in demented PD patients, while improving cognition.

Activities of Daily Living↗
PubMed1995

Tremor as a factor in prolonged reaction times of parkinsonian patients.

Prolonged reaction times and tremor are symptoms of Parkinson's disease (PD). Recently, we showed the existence of a systematic phase relationship between tremor-at-rest and the onset of voluntary motor responses in PD patients. In the present study we investigated whether this phase relationship contributes to the prolongation of reaction time in PD. Eight PD patients with prominent tremor-at-rest and five age-matched controls performed rapid stimulus-evoked index finger abductions under isometric conditions. Force and surface electromyogram (EMG) signals from first dorsal interosseus muscle were recorded and analyzed off-line by means of automatic routines. Reaction times of PD patients exhibited a significant dependence of mean values and variability on the current tremor phase at the onset of the voluntary motor response. Responses with an onset of contraction during the beginning of an EMG tremor burst were substantially delayed (on average 50 ms) and showed more variability in comparison to responses initiated at later times in the tremor cycle. This effect can be modeled by a simple gating process splitting the tremor cycle into two different system states that supports and inhibits the initiation of voluntary motor responses, respectively. We conclude that attraction of voluntary motor initiation to the tremor oscillator clearly contributes to prolongation of reaction time in PD.

Aged↗
PubMed1995

Statistical prediction of the optimal site for thalamotomy in parkinsonian tremor.

Stereotactic lesions in the thalamus for treatment of parkinsonian tremor are often made at the location where neurons fire at approximately tremor frequency (tremor cells). Some of these cells show a large amount of activity at tremor frequency and are significantly correlated with electromyographic activity (EMG) during tremor. Our analysis of cellular location identifies a cluster of neurons showing activity characterized both by concentration of power at tremor frequency and by significant correlation with EMG. In a retrospective analysis of results in 15 patients, lesions placed within 2 mm of the center of this cluster were uniformly effective in relieving tremor. Therefore, a small lesion targeting this cluster is effective in treatment of parkinsonian tremor.

Brain Mapping↗
PubMed1998

Improvement of action tremor by chronic cortical stimulation.

The authors present a patient who had long-term improvement of a severe upper limb action tremor after chronic cortical stimulation. A 40-year-old woman complained of facial pain and tremor of the left arm after removal of an acoustic neurinoma. A motor cortex stimulation was performed to treat the deafferentation facial pain in 1993. Chronic cortical stimulation induced complete relief of both pain and tremor and allowed the patient to recover functional capacity of the limb. These effects persisted throughout a 32-month follow up. Differential effects on pain and tremor were observed when parameters of stimulation were varied, suggesting different mechanisms for the relief of pain and tremor. Attention was focused on control of the tremor. This effect could be the result of the inhibition of subcortical structures which are involved in tremor. Chronic cortical stimulation appears to be an effective treatment for controlling severe action tremors.

Activities of Daily Living↗
PubMed1998

Animal models of action tremor.

This article is devoted to animal models of tremors that emerge from lesions in the Guillain-Mollaret triangle. Cerebellar intention tremor is caused by lesions in the brachium conjunctivum or in the interpositus nucleus, possibly in combination with damage to the dentate nucleus. Impaired feed-forward motor control delays the braking of rapid movements, resulting in target overshoot and subsequent oscillation. Transcortical and transcerebellar sensorimotor loops undergo oscillation at a frequency that depends on the mechanical properties of the limb and the length of the sensorimotor loop (mechanical reflex oscillation). The crescendo quality of intention tremor may be a result of amplification of tremor in reverberating brain stem-cerebellar or thalamocortical loops. So-called rubral or midbrain tremor is caused by a combination of damage to the brachium conjunctivum and nigrostriatal pathways in the vicinity of the red nucleus. Secondary compensatory changes in the motor system are probably involved because midbrain tremor in people usually begins weeks or months after a midbrain stroke or trauma. Harmaline causes enhanced neuronal synchrony and rhythmicity in the inferior olive; this animal model, although as yet unproven, is the most popular one for essential tremor (ET). Additional studies in laboratory animals are needed to define the seemingly universal involvement of the cerebellum and ventrolateral thalamus (ventralis intermedius [Vim]) in virtually all human tremor disorders.

Cerebellum↗
PubMed1998

Long-term measurement of tremor.

To account for the fluctuating and context-dependent nature of tremor, the method of ambulatory long-term electromyography (EMG) was developed for quantification of this symptom. It is based on successive evaluation of 15-s intervals by using a fast Fourier transformation (FFT). The standard results obtained are (a) tremor occurrence, a measure of how many intervals contain tremor; (b) mean tremor intensity; and (v) mean tremor frequency. This new method fulfills the so-called "test criteria" such as reliability, validity, sensitivity, and specificity for tremor quantification in essential tremor (ET) and Parkinson's disease (PD). In addition, we developed a method of determining the antagonist activation pattern by using cross-correlation analysis, also based on the long-term approach. This allows differentiation between ET and PD with a high sensitivity and a high interrater reliability. We conclude that long-term EMG is useful for both quantification and differentiation of tremor.

Diagnosis, Differential↗
PubMed1998

The subthalamic nucleus and tremor in Parkinson's disease.

The role of the subthalamic nucleus (STN) in the origin of parkinsonian tremor is discussed. Previous studies in monkeys made parkinsonian by MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) administration suggested a direct participation of the STN in the pathophysiology of tremor. We recorded tremor-related activity in the STN in 12 patients with Parkinson's disease (PD) and found that microstimulation of the sensorimotor region of the nucleus, where these neurons are present, stopped the tremor with a very short latency. Long-term treatment by means of bilateral deep-brain stimulation (DBS) in the same 12 patients led to a significant reduction of tremor as well as other cardinal features of PD. This effect was blindly assessed at 3 months after implantation. In another group of seven patients, a unilateral lesion of the STN was performed. Both postural and resting tremor were significantly improved on the limbs contralateral to the lesion side. In three patients, tremor disappeared completely after 12 months of follow up. The electrophysiologic data and therapeutic effect of inactivating the STN strongly indicated that this structure is directly involved in the origin of parkinsonian tremor, as suggested by the MPTP model.

Adult↗
PubMed1993

Tremor reduction by microinjection of lidocaine during stereotactic surgery.

We report our experience with lidocaine microinjection into the thalamus in 10 patients undergoing stereotactic thalamotomy for the treatment of Parkinsonian or non-Parkinsonian tremor. 18 injection sites in 4 patients with Parkinson's disease and 22 sites in 6 patients with other forms of tremor have been compared with respect to the effect of microstimulation. In over two thirds of cases the test microinjection replicated the effects of microstimulation. Long term follow up will be required to determine whether lesions made on the basis of lidocaine induced tremor suppression will result in a lower rate of tremor recurrence than those based on stimulation induced tremor suppression. In those patients in whom stimulation induced tremor suppression occurs but tremor arrest cannot be produced with lidocaine microinjection, chronic thalamic stimulation may be an alternative for the long term control of tremor in these patients.

Electric Stimulation Therapy↗
PubMed1996

Tremor and voluntary repetitive movement in Parkinson's disease: comparison before and after L-dopa with positron emission tomography.

Brain regions involved in tremor and voluntary movement were compared in seven subjects with hemiparkinsonian tremor using positron emission tomography and the [15O] water bolus activation method. Repeated measurements of the regional cerebral blood flow were performed both before and after tremor arrest induced by administration of L-dopa as well as during voluntary repetitive movements of the hand contralateral to tremor side. The normalized regional cerebral blood flow (NrCBF) was measured in regions of interest with anatomical boundaries that were defined for each subject by means of a three-dimensional reconstruction of magnetic resonance imaging data. Taking the rest after L-dopa as a control condition, NrCBF increased during tremor in a network of regions including the precentral (mean +/- SD 5.36 +/- 4.6%, P = 0.006) and paracentral (6.11 +/- 6%, P = 0.01) gyri contralateral to tremor side, the supplementary motor area (SMA; 4.03 +/- 4%, P = 0.02, n = 8 pairs), and the cerebellar vermis (8.64 +/- 9.9%, P = 0.01, n = 12). During voluntary repetitive movement of the hand contralateral to tremor compared with rest after L-dopa, the same patients activated the precentral (8.25 +/- 2.6%, P = 0.0006) and postcentral regions contralateral to movement (8.43 +/- 3.7%, P = 0.002), and the cerebellar cortex (3.49 +/- 2.1%, P = 0.03), precentral (3.58 +/- 3.1%, P = 0.04), and paracentral (4.03 +/- 3.6%, P = 0.04) regions ipsilateral to movement. The cerebellar vermis was activated (8.15 +/- 5.6%, P = 0.02, n = 8) as well as the SMA, but not significantly at the 0.05 level (5.16 +/- 5%, P = 0.08, n = 5). These results confirm the similarities of brain structures involved in parkinsonian tremor and voluntary movement and provide an anatomofunctional substrate for their clinical interactions.

Aged↗
PubMed1983

Exploring the functional significance of physiological tremor: a biospectroscopic approach.

The functional significance of physiological tremor - the high frequency (8-12 Hz), low amplitude oscillation that occurs during the maintenance of steady limb postures - is not known. Often tremor, perhaps because of its pathological manifestations, is considered a source of unwanted noise in the system, something to be damped out or controlled. An examination of the phase relationship between tremor and rapid voluntary finger movement in normal subjects suggests a very different view. In four experiments in which tremor displacement and accompanying electromyographic activity were simultaneously monitored, we show a clear and systematic relationship between tremor and movement initiation. Empirically obtained frequency distributions of tremor peak-to-movement initiation time were most closely aligned to a probability density function (derived via numerical integration techniques) that assumed movements were initiated when the muscle-joint system possessed peak momentum. This relationship - evaluated by Chi-square goodness-of-fit tests - was evident regardless of whether the movements were self-paced (Experiments 1 and 2) or in response to an auditory reaction time signal (Experiments 3 and 4). The addition of a load to the finger in Experiments 2 and 4, though tending to reduce tremor frequency, did not prove disruptive, nor did a fractionated reaction time analysis reveal any significant inertial contribution to the maintenance of the phase relationship. These data are consistent with an emerging view that the motor control system is sensitive to its own dynamics, and suggest that under certain conditions normal physiological tremor is a potentially exploitable oscillation intrinsic to the motor system.

Electromyography↗
PubMed1981

Quantification of tremor in rats induced by physostigmine.

A simple and accurate device for recording tremor intensity in unanaesthetized and unrestrained rats is described. The physical measures of tremor are shown to have several advantages over previous devices. First, the new apparatus, unlike some earlier ones, does not restrict the animal's movements to an unusually small cage, with weighty mechanical devices or with electrical leads. Second, most earlier methods for measuring tremor use a subjective rating scale. However, the present method uses objective and reliable measures. In a double-blind, illustrative experiment involving complete crossover, Wistar rats were randomly injected IP with physostigmine in doses of 0.2, 0.4, 0.6 and 0.8 mg/kg or the corresponding amount of 0.9% NaCl solution as control. The recorded tremor intensity showed a clear dose-response relationship for physostigmine. Moreover, linear regression of the dose-response relationship showed that tremor intensity increased linearly with increasing doses of physostigmine. The cholinergic antagonist atropine (0.3 mg/kg SC) antagonized physostigmine-induced tremor, whereas methylatropine (0.3 mg/kg SC) tended to potentiate it. These results show that the technique described is suitable for quantification of tremor intensity in rats and for testing drug interactions on physostigmine-induced tremor.

Animals↗
PubMed2001

The relationship between physiological tremor and the performance of rapid alternating movements in healthy elderly subjects.

The power distribution in the frequency spectrum of tremor is known to vary among individuals and its median power frequency declines with ageing. The purpose of the present study was to determine whether a reduction of the central component of physiological tremor would correlate with a reduction of motor performance. Then, the power distribution in the frequency spectrum of tremor from limb extremities might serve as an index of neural drive in healthy elderly subjects. Rest tremor, postural tremor from the finger, and pronation-supination at the wrist were recorded in 102 healthy nuns living in a convent (mean of 72+/-12 years). Results reveal that several elderly subjects possessed a power distribution of tremor very similar to that of much younger subjects (mean 27 years+/-3 SD), showing a preponderance of power within the 7.6- to 12.5-Hz band. Duration of pronation-supination cycles of these elderly subjects was, however, similar to that of other elderly subjects who had a preponderance of power within the 3.6- to 7.5-Hz band. Consequently, healthy elderly subjects who possessed a predominance of power within higher frequencies were not at an advantage over other healthy elderly subjects when performing a pronation-supination task. The age of subjects was, however, a better predictor or motor performance. In conclusion, the present findings suggest that, under normal physiological conditions, a reduction of the central component of physiological tremor does not induce a reduction of motor performance. Consequently, tremor recorded at limb extremities cannot be used as an index of neural drive.

Aged↗
PubMed2005

Difference in surgical strategies between thalamotomy and thalamic deep brain stimulation for tremor control.

Stereotactic targeting strategies differ between thalamotomy and thalamic deep brain stimulation (DBS) for tremor control. In thalamotomy, a minimal radiofrequency lesion created within the lateral portion of the nucleus ventralis intermedius (Vim) often affords the best control of parkinsonian tremor, supporting the assumption that there is a concentrated cluster of cells within this area which is responsible for tremor. However, this assumption may not always be true; such neural elements sometimes appear to spread out across wide areas. Cells with tremor-frequency activity are widely distributed over the areas extending from the Vim to the nuclei ventralis oralis posterior and anterior (Vop and Voa). All of these cells appear to be more or less involved in tremor generation, especially in patients with essential tremor and post-stroke tremor. In contrast to radiofrequency lesions for thalamotomy, electrodes for DBS can be arranged in such a way that wide areas can be stimulated, if necessary. For this purpose, it is critically important to determine optimal placement and orientation of DBS leads for arranging the electrodes to yield maximal benefits in patients with tremor.

Deep Brain Stimulation↗
PubMedDate not supplied

Bilateral organization of physiological tremor in the upper limb.

The bilateral patterns of physiological tremor in the upper limb of adults were examined under conditions where eight combinations of the elbow, wrist and index-finger joints of the right arm were braced using individually molded splints. The hypotheses tested were that: (a) coordination of upper-limb tremor involves (compensatory) coupling of intra- but not inter-limb segments, (b) splinting the respective joints of the right arm changes the organization of this synergy in both limbs, and (c) reducing the involvement of joint-space degrees of freedom through restricting their motion (by splinting) results in increased tremor in the distal segments. Under no-splinting conditions, significant relationships were only observed between adjacent (intra-limb) effector units, with the strength of the correlation increasing from proximal to distal. Splinting the right limb resulted in an increase in the strength and number of significant intra-limb relationships in both limbs. No inter-limb tremor relationships were found between any segment during this task, irrespective of the splinting condition. The frequency profile for the tremor in each limb segment showed two prominent frequency peaks (at 2-4 Hz and 8-12 Hz). A third, higher frequency peak (18-22 Hz) was observed in the index fingers only. Splinting the right limb produced a general increase in the amplitude and variability of tremor in the fingertip of both arms. This effect was particularly strong under conditions where the more proximal joints were splinted. The lack of any between-limb relationships, coupled with the fact that splinting one limb influenced both limbs, suggests that some form of linkage does exist between the limbs. It is unlikely that mechanical linkages can explain fully these relationships. It is proposed that the tremor observed in either limb represents the output of a central oscillatory mechanism(s), but that this output is subsequently independently filtered in a parallel fashion on its way to each respective limb. A common bilateral (compensatory) strategy is employed to minimize the tremor in either limb during this multiple-degrees-of-freedom task.

Adult↗
PubMed2006

Kinetic tremor in Parkinson's disease--an underrated symptom.

Since the first description of the disorder which we now call "Parkinson's Disease" (PD) much has changed not only because of new therapeutic possibilities. Initially only the rest tremor was described. Today it is generally accepted that PD can be accompanied by different forms of tremor. Nevertheless the kinetic tremor is hardly examined and no attention is paid to it in clinical rating scales although it can already be found in old published drawings of PD-patients. To date instrumented investigations do not capture the most common kinetic tremor of PD that seems to be frequent under everyday life conditions. In order to assess the significance of kinetic tremor in PD, tremor during a spiral drawing task was investigated in an open study involving 870 patients. The results indicate that a combination of rest, postural and kinetic tremors constitute the most frequent tremor constellation in PD.

Adolescent↗
PubMed1980

Synchrony among rhythmical facial tremor, neocortical 'alpha' waves, and thalamic non-sensory neuronal bursts in intact awake rats.

A fine (approx. 9 c/sec) tremor of the jaw and/or vibrissae was observed in normal rats while they were standing still and not showing gross bodily movement. The tremor was distinctly different in frequency, intensity, and behavioral context, from movements involved in gnawing, tooth chattering, or exploratory sniffing. Individual tremor movements (recorded as EMG) occurred in synchrony with individual bursts of multiunit activity (MUA) recorded in the ventrobasal complex of the thalamus and with individual 'spikes' in the cortical (frontal-occipital) EEG. Single trains of this rhythmical activity often lasted more than a minute. The phase relationships between EMG and MUA differed among individuals, but tended to remain consistent within each individual. Movement artifacts were ruled out since (1) the moments of occurrence of individual tremor movements and MUA bursts were interdigitated rather than simultaneous, and (2) during high amplitude EMG bursts accompanying sni ffing (associated with EEG theta rhythm), tooth chattering, eating or licking, no corresponding activity in the MUA was observed. We also ruled out the possibility that the neural activity was generated by reafference, for (1) during vigorous non-tremor sniffing movements of the vibrissae, or chattering or chewing movements of the jaws, the rhythmical MUA was absent (although the units did discharge if the vibrissae contacted an obstacle or were brushed by the experimenter), (2) rhythmical MUA often continued both during brief pauses in the motor tremor, and in its absence, and (3) injection of Xylocaine s.c. into the face abolished sensory responses of the thalamic units, but the rhythmical MUA persisted. We discuss evidence which suggests that (1) the rhythmical cortical EEG waves are the equivalent in the rat of the alpha (mu) rhythm, and (2) the existence of parallels between alpha-tremor and Parkinsonian tremor in terms of their mechanisms and functions.

Alpha Rhythm↗