Dynamic synchronisation of central oscillators in essential tremor.

OBJECTIVE: Coherence analysis of electromyography (EMG) signals in essential tremor (ET) suggests that tremor in the right and left arm is induced by independent central oscillators. The sensorimotor cortex seems to be part of the tremor-generating neuronal network in ET. Here, we investigated using electroencephalography (EEG) whether the independence of central oscillators in ET is supported by the analysis of cortical activity. METHODS: In 8 patients with ET, bilateral hand tremor was activated by wrist extension. EMGs from the wrist flexors and extensors were recorded simultaneously with an EEG. EEG-EMG coherence was estimated for 74 epochs of 60 s duration. RESULTS: In 42.6% of the cases, EEG-EMG coherence at the tremor frequency existed only with the contralateral sensorimotor cortex. However, 21.6% of the tremor-EMGs were coherent with EEG activity over both the contralateral and ipsilateral sensorimotor cortex. Bilateral and exclusively contralateral EEG-EMG coherence could alternate within the same recording. Bilateral EEG-EMG coherence was associated with increased right-left EEG-EEG coherence, increased right-left EMG-EMG coherence as well as with increased tremor strength. CONCLUSIONS: In ET, central oscillators in the right and left brain are not entirely independent of each other. They may dynamically synchronise, presumably by interhemispheric coupling via the corpus callosum.     

"Rubral" tremor induced by a neuroleptic drug.

"Rubral" tremor is a rare movement disorder that occurs typically with midbrain damage. It is defined by its presence at rest, with sustained posture, and with movement. Whether it is a single-tremor disorder or a combination of two distinct tremors is debated. This report chronicles a severe neuroleptic induced "rubral" tremor in a patient who had had a stable posttraumatic ataxia. The dramatic response to benztropine and bromocriptine is illustrated in the videotape.     

Fast and slow twitch units in a human muscle

A study has been made of the isometric twitches of single motor units in the extensor hallucis brevis (EHB) muscle in man. The twitch contraction times ranged from 35 to 98 msec and the pooled results indicated the presence of at least two types of unit. The recorded twitch tensions also varied considerably (from 2 to 14 g) but were not related to the twitch speeds. The twitch tension developed by the whole EHB muscle depended on the initial length of the muscle and on the age of the subject. The EHB muscle was estimated to contain approximately 56 motor units.     

Postural tremor induced by paint sniffing

Volatile substance abuse is the intentional inhalation of volatile solvents, aerosols, gases or nitrates for the purpose of intoxication. This practice is more common among young people, due, in part, to the low cost and ready availability of these inhalants. In this report, we present the case of a 22-year-old male with a seven-year history of chronic paint sniffing. The patient presented with vigorous postural and kinetic tremor in both hands. A neurological examination revealed a bilateral, non-fatiguing geotropic positional nystagmus and a mild ataxia together with dysdiadochokinesis. He also had a mild chronic encephalopathy. Following treatment with clonazepam, the tremors subsided, but were not completely controlled.     

Impairment of post-movement beta synchronisation in parkinson's disease is related to laterality of tremor.

OBJECTIVE: Post-movement beta synchronisation (PMBS) is a physiological indicator of the activity of movement related neural networks. To investigate the pathophysiology of this phenomenon, we examined its characteristics in patients with unilateral tremor-dominant Parkinson's disease (PD). METHODS: Movement duration and PMBS was measured after self-paced movement of the thumb at movement-reactive beta frequencies, over the supplementary motor area in 10 PD patients and 8 control subjects. RESULTS: Movement duration in PD patients was longer than in controls. In left hand tremor patients, movement of the left hand was significantly longer compared to the right hand. When PD patients moved their non-affected hand, similarly to the controls, PMBS was higher contralateral to the movement. After movement of the tremulous hand, the contralateral PMBS decreased significantly and the contralateral preponderance disappeared. In the same hemisphere, PMBS was higher after contralateral to the non-affected hand movement, than after ipsilateral to the tremulous hand after movement. CONCLUSIONS: PMBS in PD is affected by the activity of tremor related neural networks, suggesting that both cortical and subcortical sources are responsible for its generation. Examination of PMBS in various neurological diseases might provide further data on its physiological significance.     

Dystonia and tremor induced by peripheral trauma: predisposing factors.

Movement disorders are usually of central origin, but sometimes involuntary movements occur after peripheral trauma. Twenty eight patients, 13 women and 15 men, mean age 37 years (range 15-78), were studied with dystonia or tremor in whom the onset of abnormal movements was related, in time and in distribution, to injury of a body part. Among 23 patients with latency of less than one year after injury, focal dystonia of the involved body part was found in 18, nine of whom had associated reflex sympathetic dystrophy (RSD). One of five patients with peripherally induced tremor had RSD. Abnormal electromyography or nerve conduction velocities were found in the affected limb in four patients, but other electrophysiologic techniques provided evidence for disturbed central function. In 15 patients (65%) possible predisposing factors may have contributed to the pathogenesis of the trauma induced abnormal involuntary movements.     

New muscle transplant method produces normal twitch tension in dystrophic muscle.

Grafting newborn muscle is an innovative method of muscle transplant. This method overcomes hypoxia in the deeper fibers and facilitates reinnervation and revascularization of the grafted muscle fibers, thus promoting the survival and development of the characteristics of the donor muscle. The result achieved is superior to that obtained from mature muscle grafts or from minced muscle transplants. When an intact soleus from a 1-day-old normal mouse was grafted into a recipient soleus of a 20-day-old dystrophic C57BL/6J-dy2J mouse, the actively developing normal graft helped to improve the structure and function of the dystrophic muscle. When compared to the intact dystrophic solei, the test dystrophic muscles five to six months after operation showed increases in cross-sectional area, in wet weight, in twitch and tetanic tension, and in the number of muscle fibers with high resting membrane potentials. This is the first procedure to have raised the muscle twitch tension in an adult dystrophic mouse to the normal level.     

Intermittent tremor-bursts induced by chlorpromazine and pentobarbitone in guinea pigs: a new tremor model.

It was discovered by serendipity that a combined application of chlorpromazine (3.5 mg/kg) and pentobarbitone (20.0 mg/kg) induced intermittent tremor-bursts in four extremities of guinea pigs. This tremor with a prominent extensor activity disappeared after spinalization, indicating a supraspinal process. Biperiden reduced the frequency and amplitude of the tremor, which was further diminished by amantadine. Baclofen was found to be most potent drug in suppressing tremor. It was suggested that the cortico-striato-pallido-thalamo-cortical feedback loop may be impaired by a combined action of chlorpromazine and pentobarbitone. This new animal model for drug-induced tremor would be of considerable importance with regard to physiological, biochemical, pharmacological and pathological aspects of motor control.     

A simple tremor model induced by pentobarbitone in guinea pig.

We have recently reported that a combined application of chlorpromazine and pentobarbitone induced intermittently occurring tremor bursts in guinea pigs (Tan et al., in press). This was a chance discovery. It will be shown in the present work that chlorpromazine is not essential for this postural tremor; only pentobarbitone in low dosages produced intermittent tremor bursts in guinea pigs lying in a supine position. Chlorpromazine alone was not effective in producing tremor. The pentobarbitone-induced tremors were attenuated by the i.v. application of biperiden or lioresal. These results indicate that these tremors would be produced by the basal ganglia as in Parkinsonism.     

Loss of twitch torque following muscle compression

With the elbow flexed, compression of the human biceps brachii has been found to reduce twitch torque, with an approximately linear relationship being observed between the loss of torque and the applied pressure (up to 45 kPa). The decline in torque could no longer be demonstrated when the biceps muscle was stretched, by extending the elbow from a flexed position. The loss of torque in the flexed position appeared to be due to an inability of muscle sarcomeres to bulge sufficiently to take up the series elasticity at the fiber ends. © 1997 John Wiley & Sons, Inc. Muscle Nerve, 20, 167–171, 1997.     

Parkinsonian-like tremor induced by a combined application of chlorpromazine and pentobarbitone in cats with left-paw preference.

A Parkinsonian-like tremor can be induced by a combined application of chlorpromazine and pentobarbitone in cats. Interestingly enough, only cats with left-paw preference were found to have a predisposition to this drug-induced tremor. The cats with ambidexterity and right-preference in paw use did not show any visible tremorogenic action of these drugs. Especially the proximal muscles of all four extremities showed oscillations with a frequency of about 12 per second in all animals tested, which completely disappeared after i.v. application of lioresal, atropine and biperiden. It was suggested that this new drug-induced tremor model may reflect an impairment within the cortico-striato-pallido-thalamo-cortical feedback loop. It was also concluded that left-handers may have an increased predisposition to centrally acting drugs than nonleft-handers.     

Upper limb tremor induced by peripheral nerve injury

We report a patient with proximal right upper limb tremor, secondary to direct peripheral nerve lesion caused by prior thoracic surgery. Electromyography demonstrated neurogenic abnormalities and tremor in muscles innervated by the thoracodorsal and long thoracic nerves. Somatosensory evoked potentials, transcranial magnetic stimulation, and MRI of the cervical and thoracic spine were normal. Tremor persisted in REM and non-REM sleep. These findings suggest a peripheral generator.     

Regeneration of frog twitch and slow muscle fibers after mincing

Iliofibularis muscles of Rana temporaria were minced and allowed to regenerate in the iliofibularis or the sartorius bed of the same frog. Regenerated muscles were examined for the presence of slow muscle fibers using electrophysiologic, histochemical, and contractile parameters. Muscle regeneration from sartorius mince was also studied. Regeneration was more successful from iliofibularis than from sartorius mince, and the iliofibularis bed was more favorable for regeneration than the sartorius bed for both types of muscle. Twitch fibers regenerated within a few months, but slow fibers could not be identified earlier than 14 months after muscle destruction. Slow muscle fibers regenerated only from iliofibularis mince, both orthotopically and heterotopically. All regenerates capable of maintaining a K-contracture contained histochemically identified slow fibers; the membrane properties of electrophysiologically identified slow fibers were normal. It is concluded that slow muscle fibers regenerate only from the remnants of a muscle that contains slow fibers. The results are discussed with respect to the role of innervating nerve fibers.     

Prolongation of twitch potentiating mechanism throughout muscle fatigue and recovery

Measurements have been made of twitch amplitudes in human ankle dorsiflexor muscles during and following fatiguing electrical stimulation. In six subjects, studied with the arterial circulation occluded, the twitch was observed to undergo an early potentiation (mean, 99 +/- 50%) followed by complete disappearance. A second, smaller phase of potentiation (mean, 25 +/- 30%) occurred during recovery and gave way to prolonged depression of the twitch. A comparison of these results with those obtained with an intact circulation suggested that the four phases in the behavior of the twitch were the net result of two processes, potentiation and fatigue, with different time courses. Provided they are timed appropriately, observations of twitch amplitude can provide useful information concerning the development of, and recovery from, muscle fatigue.