Tremor is an approximately rhythmic, roughly sinusoidal involuntary movement. Despite nearly a century of modern clinical and laboratory investigations, no tremor is understood completely. Human tremors derive from different etiologies and thus, not suprisingly, the physiologies are diverse. Tremors may derive from mechanical oscillations, mechanical reflex oscillations, normal central oscillators, and pathologic central oscillators. However the definitive identification of oscillators for any tremor have not yet been established. Measuring tremor clinically is difficult because tremors behave in different and often complex ways. There are several different techniques for measuring tremor. One of most popular and sensitive methods use accelerometries. An excellent method consists of accelerometry and EMG combined with spectral analysis and weighting of the body part, which allows separation of tremors coming from mechanical reflex and central oscillators. Now times, increased power and speed of microprocessors enable clinical laboratories to quantify tremor and other aspects of motor disability with accuracy and precision not possible a decade ago.

Purpose
: Primary writing tremor(PWT) can be classified as either type A or type B depending on whether tremor appeared during writing or whilst writing and also on adopting the hand postures normally used for writing. Through the clinical experience author has had an impression that PWT type B may not be purely dependant on specific writing postures. The objective of this study was to clarify whether PWT type B have writing posture-specificity or nor. Results : The data indicated that type B PWT is not writing posture-specific. Various pronation and supination postures could evoke tremor as well as writing postures. Furthermore most of other pronation-and supination-related tasks could evoke tremors as well as action of writing. Conclusions : The present data suggest that PWT should be limited only on the pure form of task-spesific PWT type A.

Purpose
: The pathophysiology of essential tremor(ET) remains unknown. PET studies of ET showed some conflicting data. One study reported significant glucose hypermetabolism of the medulla and thalami, but other studies reported abnormal bilateral overactivity of cerebellar and red nuclear connections. The previous experimental studies suggested that each PET finding reflects a part of neural circuit which is responsible for ET. So it can be imagined that olivocerebellar oscillation may be transmitted by the way of cerebellar projections to the thalamus in ET. It has been reported that the cerebellar dentate nucleus neurons are involved in the generation and/or guidance of movement based on visual cues. The purpose of this study is to clarify the role of dentato-thalamic tract in ET. Methods : Tremor amplitudes were recorded as each patient perform two kinds of task, one involving sensory-guided movement and the other involveing memory-guided movement. Each patient was asked to perfome the same movements with his/her eyes closed ET. Results : The results showed that average amplitudes of tremor were significantly higher during visually guided task than during memory guided task in ET patients. Conclusions : Our results led us to conclude that dentato-thalamic tract might be related to the control of tremor I ET.

Introduction : Orthostatic tremor develops in the legs while standing up with no weakness, pain or imbalance in theleg and the tremor is characteristically not observed when walking. However there have been some confusions aboutorthostatic tremor in several aspects. For the past ten years, we have observed 4 patients with orthostatic tremor. In eachcase tests were performed to investigate the following three important areas of inquiry about orthostatic tremor. Firstly,whether this disorder is an independent diagnostic entity or a variant of essential tremor. Secondly, whether the progressof this disorder is specifically related with standing posture. Lastly, the nature of the pathophysiologic mechanismbehind the appearance of the tremor when standing after the lapse of a certain latent period and its disappearance uponthe commencement of walking.Methods : Our 4 cases of orthostatic tremor were studied clinically, electrophysiologically, and pharmacologically.Electrophysiological tests included tremor spectrum test and electromyography.Results : We observed the presence of this tremor in several other tonic postures, as well as its absence, in a verticallylifted position from all our cases. Our cases registered a variable tremor frequency between 5 and 12 Hz according tothe tremor spectrum test and EMG. Furthermore all our 4 cases demonstrated patterns of both synchronous EMG activityand alternating EMG activity at various times in homologous muscles of both legs. Orthostatic tremor was improvedsignificantly with propranolol as well as clonazepam.Conclusions : From the results of our study we drew the following conclusions. It is probable that orthostatic tremoris simply a variant of essential tremor rather than being an independent diagnostic entity and that in most cases itsdevelopment is specifically related with muscle contraction rather than merely with the act of standing. Furthermore wediscovered a clue in the previously described neural control mechanism that the nuclear bag fibers in the muscle spindlehave lag time of several seconds in their response to muscle strength and that their baseline does not reset fully in rapidlymoving muscle. This neural control mechanism could offer sufficient explanation for the phenomena of tremorappearance when standing and disappearance when walking in orthostatic tremor.

Abnormal writing can result from a large variety of neurologic disorders of motor control. Primary writing tremor(PWT) in its pure form denotes occurrence of a disabling tremor induced by writing alone. Therefore PWT is typical task-specific tremor. PWT could be classified as either type A or type B. In a strict sense, type B PWT is not pure form of PWT because it is not task specific. We describe a case of PWT type A. A 53-years-old right handed policeman complained of a 4 years history of shaking of his right had that interfered with writing. Tremor appeared during writing but not on adopting the hand position normally used for writing.

Background
: Tremor is uncommon manifestation of stroke. Therefore a few cases have been reported until now. There is still uncertainly about the characteristics of post-stroke tremor. Furthermore the pathogenesis and responsible structures of post-stroke tremor are not precisely known. We have recently experienced 34 cases of post-stroke tremor for the past 6 years. We analysed the clinical features and electrophysiologic findings of post-stroke tremor to evaluate the general characteristics and to analogize the possible pathogenetic mechanisms of post-stroke tremot. Methods : The clinical characteristics of post-stroke tremor were summarized in according to the onset time, involved body parts, types, tremor frequencies, neuroradiologic findings, and associated symptoms. The tremor frequencies were recorded by using a gyroscope. The spectral analysis of tremor frequencies were done automatically with Motus I software. Results : Tremor onset were remarkably varied. Some patients showed a tremor appearing at the onset of a stroke and other patients showed delayed-onset tremor 10 years after a stroke. Tremor frequencies were also much varied. The range of hand tremor frequencies were from 1.5 to 12Hz. Lesions were found in 31 cases (infarction 27, hemorrhage 4) on neuroimaging. In the cases of cerebral infarctions, 7 cases showed multiple small vessel disease and 20 cases showed cerebral vessel lesions. The most commonly involved cerebral vessel lesion was the middle cerebral artery territory. Several different clinical patterns of post-stroke tremor were identified. Conclusions : There are some evidences fro the data summarized here to suggest that several pathogenetic mechanisms including central oscillators could be involved for the development of tremors and that tremor generating neural circuits.

It has been said that variable anatomical structures and neural circuits are related to the generation of tremor. There are cerebral cortex, thalamus, basal ganglia, inferior olivary nucleus, midbrain tegmentum, stretch reflex, and musculoskeletal structures. The stretch reflex is related with the physiologic tremor and various peripherally originated tremors. We experienced a case with the post-stroke resting tremor which was induced and aggravated by mechanical stretching stimulation. In the present case, stretch reflex has a major role in the generation and exacerbation of tremor. It is presummed that the development of tremor is attributed to the increased rhythmicity of ventral intermedius nucleus of thalamus. The enhancement of thalamic rhythmicity may be due to the increasement of long latency reflex by post-stroke rigidity. This case suggests that stretch reflex may have a major role in the pathophysiologic mechanism of a certain centrally originated tremor.

Background
Essential tremor (ET) is a common movement disorder that often causes functional disability. There have been very few investigations about the clinical characteristics of ET in Korea. Therefore, we performed a study showing the clinical features and electrophysiological findings of ET.
Methods: We analyzed medical records and accelerometry data of 152 patients (male vs female; 79 vs 73) with ET, who visited the Neurology Clinic of Hospital from 2000 to 2003. Clinical characteristics of ET were summarized including the age of onset, family history, tremor type, body part involved, and associated symptoms. The frequency of tremor was recorded and the spectral analysis of tremor was performed.
Results: The age of tremor onset showed bimodal distribution with peaks in the 2nd and 5th decades. Family history was found in 46 patients (30.3%). The patients with the family history presented earlier onset of tremor than patients without the history (mean age of onset, y: 35.2 vs. 49.9, P < 0.001). Tremor appeared most frequently in hands (94%), and followed by head (25%). In head tremor,