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The output from a motor nucleus is determined by the synaptic input to the motor neurons and their intrinsic properties. Here, we explore whether the source of synaptic inputs to the motor neurons (cats) and the age or post-stroke conditions (humans) may change the recruitment gain of the motor neuron pool. In cats, the size of Ia EPSPs in triceps surae motor neurons (input) and monosynaptic reflexes (MSRs; output) was recorded in the soleus and medial gastrocnemius motor nerves following graded stimulation of dorsal roots. The MSR was plotted against the EPSP thereby obtaining a measure of the recruitment gain. Conditioning stimulation of sural and peroneal cutaneous afferents caused significant increase in the recruitment gain of the medial gastrocnemius, but not the soleus motor neuron pool. In humans, the discharge probability of individual soleus motor units (input) and soleus H-reflexes (output) was performed. With graded stimulation of the tibial nerve, the gain of the motor neuron pool was assessed as the slope of the relation between probability of firing and the reflex size. The gain in young subjects was higher than in elderly subjects. The gain in post-stroke survivors was higher than in age-matched neurologically intact subjects. These findings provide experimental evidence that recruitment gain of a motor neuron pool contributes to the regulation of movement at the final output stage from the spinal cord and should be considered when interpreting changes in reflex excitability in relation to movement or injuries of the nervous system.

The output from a motor nucleus is determined by the synaptic input to the motor neurons and their intrinsic properties. Here, we explore whether the source of synaptic inputs to the motor neurons (cats) and the age or post-stroke conditions (humans) may change the recruitment gain of the motor neuron pool. In cats, the size of Ia EPSPs in triceps surae motor neurons (input) and monosynaptic reflexes (MSRs; output) was recorded in the soleus and medial gastrocnemius motor nerves following graded stimulation of dorsal roots. The MSR was plotted against the EPSP thereby obtaining a measure of the recruitment gain. Conditioning stimulation of sural and peroneal cutaneous afferents caused significant increase in the recruitment gain of the medial gastrocnemius, but not the soleus motor neuron pool. In humans, the discharge probability of individual soleus motor units (input) and soleus H-reflexes (output) was performed. With graded stimulation of the tibial nerve, the gain of the motor neuron pool was assessed as the slope of the relation between probability of firing and the reflex size. The gain in young subjects was higher than in elderly subjects. The gain in post-stroke survivors was higher than in age-matched neurologically intact subjects. These findings provide experimental evidence that recruitment gain of a motor neuron pool contributes to the regulation of movement at the final output stage from the spinal cord and should be considered when interpreting changes in reflex excitability in relation to movement or injuries of the nervous system.

ZusammenfassungDie meisten Bewegungen werden durch motorische kortikale Areale gesteuert, die partielle Redundanz aufweisen und über mehrere Gefäßterritorien verteilt sind. Bei Läsion der dominierenden kortikospinalen Projektion vom primär motorischen Kortex (M1) können die noch intakten motorischen Repräsentationen ihre Rolle ändern, sofern der Patient eine Strategie findet, sie zu aktivieren. Somit hängt die Prognose der motorischen Restitution ab von Lokalisation und Ausdehnung einer zentralen Läsion sowie von der Intensität und Repetition des Trainings.Neben den Neuronen des Kortikospinaltrakts tragen auch kortikostriale Projektionen zur Restitution bei. Cues wie sensorisches Feedback, propriozeptive, verbale und visuelle Reize oder bereits die Vorstellung einer Bewegung können über dieses System die Aktivität der Motoneurone steigern sowie den Abruf erlernter Bewegungsmuster erleichtern.Bei Läsion des Kortikospinaltrakts werden motorische Systeme des Mittelhirns aktiviert, beispielsweise der an der Steuerung der Lokomotion beteiligte pedunculopontine Nucleus. Dieser projiziert auch zu den Retikulo-und Rubrospinaltrakten, die eine qualitativ eingeschränkte motorische Erholung ermöglichen. Die Systeme des Mittelhirns sind auch mit central pattern generators des Rückenmarks verbunden, die neben ihrer Rolle für das Gehen auch an synergistischen Bewegungen der oberen Extremität beteiligt sein könnten. Spastische Syndrome treten vorwiegend nach nahezu kompletter zentraler Deefferenzierung mit Plegien auf. Durch ein intensives Training werden sie nicht wesentlich verstärkt, sofern eine inkomplette Parese mit verbleibender motorischer Funktion vorliegt.

Patients with essential tremor (ET) or with cerebellar lesions have in common oculomotor abnormalities, with the exception of saccadic eye movements, which do not seem to be involved in ET. Since grasping is prolonged in ET and might be related to saccadic dysmetria, we tested whether simultaneous hand pointing could unmask it. Twelve ET patients and 14 controls performed saccades with and without simultaneous pointing movements to the same targets, and with and without a gap between the disappearance of the fixation point and the appearance of the target. Eye movements were recorded with the magnetic search-coil method, hand movements with an ultrasound-emitting probe. ET patients did not have saccadic dysmetria, and contrary to normal subjects their saccadic latency did not decrease during combined eye-hand movements compared with saccades performed in isolation. Hand movements had a longer duration in ET patients, with decreased peak acceleration, an increased latency of the peak velocity, and peak deceleration. In conclusion, this first study on eye-hand coordination in ET revealed abnormal kinematic changes in the early phase of pointing movements. These changes might be related to cerebellar disease but they are independent of the intention tremor component and saccade performance.

Objective: To study the effect of ethanol on gait in patients with essential tremor (ET). Methods: Using a three-dimensional opto-electronic gait analysis system, the authors analyzed gait at free-speed walking, at a given velocity, and during tandem gait. Patients with ET with advanced disease were examined before and after a small oral dose of ethanol. The results of the patients with ET were compared with those from age-matched healthy controls (HCs). The primary outcome criteria were the number of missteps and the ataxia score during tandem gait. Results: Before alcohol, patients with ET had more missteps and an abnormal ataxia score compared with HCs. The ingestion of alcohol with a mean blood level of 0.45% led to a significant improvement of the ataxia score and the number of missteps. HCs showed a worsening of the ataxia score and an increase of the number of missteps after alcohol, which failed to reach significance. Conclusions: Orally administered ethanol improved gait ataxia in patients with essential tremor (ET). This may reflect a reversible effect of ethanol on receptors being involved in the pathology of ET. Ethanol may act via an influence of the inferior olive or directly on alcohol-sensitive γ-aminobutyric acid receptors within the cerebellum.

It has been postulated that Parkinsonian action tremor is distinct from classical resting tremor and that it may contribute to a loss of manual dexterity in Parkinson's disease. We analyzed pinch grip coordination in 20 patients with Parkinson's disease. An object with and without an additional 500 g weight was grasped, lifted and held for a short time with opposed thumb and index finger. Force sensors recorded the force exerted by both fingers. Spectral analysis of the force traces was performed. Transition times between grasping and lifting the object were measured. 18 age matched normal volunteers served as a control group. While holding the object, there were force oscillations in the 3.5-6.5 Hz band indicating (reemerging) classical Parkinsonian tremor in 65% of the patients. This was reduced to 15-20% under levodopa. Oscillations in the 6-15 Hz band were found in 30% (50% with weight) of the patients, remaining unchanged under levodopa, and in 10% (20% with weight) of the normal controls. During lift initiation, 6-15 Hz oscillations were found in all patients and the majority of controls. The band power was positively correlated with the movement transition times in the severely akinetic patients and was significantly higher than in controls. It remained unchanged under levodopa. Our data confirm that Parkinsonian action tremor activated during complex voluntary movements is distinct from classical resting tremor. It does not show a clear levodopa response but affects dextrous movement coordination when associated with clinically severe overall akinesia.

Background: Recent animal experiments suggest an important role of descending input from basal ganglia to brainstem and via the reticulospinal tract (RST) to spinal cord in the genesis of motor symptoms in Parkinson disease (PD). In humans, a marker for RST activity is Ib mediated autogenic inhibition, which is reduced in PD patients. The authors investigated the effect of high frequency stimulation of the subthalamic nucleus (STN-HFS) on autogenic inhibition in PD. Methods: In 10 controls and 10 PD patients with chronically implanted STN electrodes, the soleus H-reflex conditioned by gastrocnemius nerve stimulation (interstimulus interval 2 to 10 msec) was used to examine the effect of STN-HFS on the activity of Ib spinal interneurons. Results: STN-HFS was able to restore the abnormally reduced autogenic inhibition. The H-reflex changes during STN-HFS significantly correlated with the clinical improvement of gait and posture. Conclusions: Observed changes in spinal autogenic inhibition may allow measurement of the contribution of subcortical routes to the STN-HFS induced motor benefit in PD.

The function of low-frequency oscillations as correlates of physiological tremor in supplementary motor area (SMA) and M1 remains unclear. In epicortical recordings from M1 and SMA and surface electromyographic (EMG) recordings in an epileptic patient we found reproducibly significant coherence between all three recording sites in the 6- to 15-Hz band. The partial coherence between SMA and muscle, however, was not significant. There was a constant phase shift between SMA and M1 indicating synchronized activity. We conclude that the cortical correlates of physiological tremor may be involved in linking different cortical motor centers and might therefore play a role in cortical motor planning.

Deep brain stimulation of the subthalamic nucleus (STN-DBS) reduces akinesia in Parkinson's disease but its impact on fine motor functions was unknown. We assessed the effects of DBS and a levodopa (L-dopa) test on the timing of the precision grip in 18 patients. Improvement on UPDRS-items reflecting hand functions and the shortening of the first phases of the precision grip were more distinct in the L-dopa test than in the pure STN-DBS condition. Other akinesia items and the time for build-up of lifting force were equally improved in both conditions. This suggests that routine STN-DBS might not be equally effective on all aspects of fine motor functions.

DBS of the STN is one of the most promising new therapies for the treatment of PD. However - like many other therapies for PD - the present stage of the scientific assessment does not yet suffice the rigid criteria of evidence-based medicine. Further studies should specifically address the questions of efficacy and side effects as well as the impact on quality of life.

Deep-brain stimulation of the subthalamic nucleus appears to reduce levodopa-induced dyskinesias, but whether this effect is caused by the reduction of the total levodopa ingestion or represents a direct effect on the motor system is unknown. Precision grip force of grasping movements and levodopa-induced dyskinesias was analyzed in 10 parkinsonian patients before and after 3 months of deep-brain stimulation of the subthalamic nucleus. Peak grip force was abnormally increased before surgery in the off-drug state and, particularly, in the on-drug state (sensitization). This grip force upregulation normalized with chronic deep-brain stimulation in both conditions (desensitization). Peak-dose dyskinesias also improved, and off-dystonia was completely abolished. Mean dosage of dopaminergic drugs was reduced, but force overflow and dyskinesias were equally improved in 2 patients without a reduction. Despite the same single levodopa test dose, force excess and levodopa-induced dyskinesias were drastically reduced after 3 months of deep-brain stimulation of the subthalamic nucleus. This indicates that direct effects of deep-brain stimulation of the subthalamic nucleus on levodopa-induced dyskinesias are likely to occur. Grip force overflow is a promising parameter to study the desensitizing effect of chronic deep-brain stimulation on levodopa-induced dyskinesias.

Physiologic tremor (PT) consists of a peripheral mechanical oscillation at the limbs' resonance frequency and an independent central component in the 6-15 Hz band. This central component has mainly been attributed to spinal interneuronal systems or subcortical oscillators but more recently also to cortical rhythms. We recorded PT electromyographically and accelerometrically from different parts of the arm in parallel to epicortical recordings from grid electrodes covering the primary sensorimotor areas of the contralateral cortex in six epileptic patients. Previous bipolar electrical stimulation of the cortical electrodes resulted in a somatotopic map of the primary cortex underlying the grid. Spectral and cross-spectral analysis including coherence spectra between epicortical electrodes and EMG and the corresponding phase spectra were performed off-line. We found significant corticomuscular coherence in the 6-15 Hz range in four out of the six patients. This coherence was focal on the cortex and it was distributed somatotopically mainly within the primary motor area. The frequency band of the coherence mostly corresponding to the EMG frequency remained stable with added inertia, while the main accelerometric frequency was clearly reduced following the resonance frequency. The phase spectra between electrocorticogram (ECoG) and EMG showed a clear delay between cortex and muscle in two of the patients, which was compatible with conduction in fast pyramidal pathways. These findings indicate that the 6-15 Hz coherence between cortex and EMG reflects a corticomuscular transmission of the oscillation rather than peripheral feedback to the cortex. We conclude that cortical networks are involved in the generation of physiologic tremor.

Gait disturbances of patients with essential tremor (ET) have been described anecdotally, but have never been investigated quantitatively. Recent studies provided evidence for a cerebellar-like hand tremor in some patients with ET. Therefore, we designed a study to assess cerebellar-like abnormalities of leg function. Twenty-five patients with ET, eight patients with cerebellar diseases (CD) and 21 age-matched healthy subjects were studied for their normal and tandem gait using a three-dimensional gait analysis system. During normal walking, CD and ET patients showed only slight abnormalities. However, ET patients exhibited abnormalities in tandem gait with an increased number of mis-steps and a broad-based, ataxic and dysmetric gait which was indistinguishable from the findings in CD. When ET patients were separated into groups of those with or without intention tremor of the hands, the gait disorder was found to be much more pronounced in the intention tremor group. Patients with this gait disorder were more severely disturbed in their activities of daily living, and suffer from an advanced stage of ET. The present results quantitatively describe a gait disturbance in advanced ET which affects tandem gait, but leaves normal gait almost unaffected. This is strong evidence for a cerebellar-like disturbance in ET.

The aim of this study was to quantify the tremor of the hand during a natural movement (kinetic tremor) in tremor-dominant parkinsonian patients (n = 13). We used a three-dimensional camera system to kinematically analyze rest and kinetic tremors in an unrestrained reach-to-grasp movement, and additional tremor recordings were performed under standard postural and rest conditions using electromyography and accelerometry. The standard analysis showed a highly synchronized tremor with similar frequencies at rest and in sustained postural tasks, with and without loading. A kinematic recording was used to compare rest and action conditions. A strong inhibition of the resting tremor was present at the onset of the movement and reached its peak during deceleration. A kinetic tremor of low amplitude was present in most of the parkinsonian patients, but its occurrence was confined mainly to the terminal periods of the movement. The frequency of kinetic tremor was significantly higher than that at rest, before the onset of the movement in Parkinson's disease, as determined by the kinematic analysis (mean, 5.5 Hz vs 6.5 Hz; p

Objectives : It has been well established that peripheral mechanical resonant factors as well as central mechanisms may play a role in the generation of physiological tremor (PT). Furthermore it has been postulated that subject's attributes like age and sex might influence PT. The present study was designed to quantify these influences on PT in a large normal population. Methods : Physiological hand and finger tremors were measured in a group of 117 normal subjects between 20 and 94 years of age using accelerometry and surface EMG recordings from the forearm flexor and extensor muscles. The hand tremor was measured in a postural position with and without weight, and the finger tremor was recorded with the arm outstretched, forearm supported and hand supported. Hand volume and grip force were measured in each subject. Results : Hand tremor frequency (mean 7.7 Hz) was reduced significantly by added inertia (mean 5.2 Hz) and it was negatively correlated with hand volume while there was no correlation with grip force. Finger tremor showed, subject to the arm position, maximally 3 and at least two distinct frequency bands (1–4, 6–11 and 15–30 Hz) reflecting the resonance frequencies of the whole arm, the hand and the finger, respectively. A significant EMG peak was found in 50–80% of the recordings. This EMG synchronization gave rise to a corresponding accelerometer peak or a significant EMG-EMG coherence in about one-third of the population indicating a central component of PT because its frequency was unaffected by mechanical changes in the periphery. We did not find a significant influence of age on the tremor frequency, while the sex of the subjects slightly but significantly changed the frequency range of hand tremor. Multiple partial correlations revealed, however, that the only direct influence on hand tremor frequency is the hand volume indicating that the influence of sex on hand tremor frequency is an indirect effect produced by the significantly larger hands of male subjects. Conclusions : In conclusion, the main determinants of PT are the mechanical properties of the oscillating limb. Apart from the dominating peripheral resonance mechanism we found indications of an additional central component of PT in about one-third of the normal population. There was no age dependence of tremor frequency and it was shown that the influence of the subjects' sex on tremor frequency only represents an indirect mechanical effect.

The tremors of Parkinson's disease (PD) and essential tremor (ET) are traditionally considered to depend on a central oscillator producing rhythmic activation of the motoneurones of all extremities. To test this hypothesis, we have compared electromyographic tremor activity in different muscles of the affected limbs using cross spectral analysis, including coherence and phase. Surface electromyographic recordings from both arms, legs, and the neck were analyzed in 22 patients with PD and 28 patients with ET. Volume conduction between neighboring muscles producing artificial "coherence" has been found to be an important methodologic problem. We have developed a mathematical test to exclude data that could distort the results. According to this test, 10% or 25% of muscle combinations from the same limb had to be excluded from further analysis in PD or ET, respectively. In both, patients with PD and ET, we found a considerable number of muscle combinations oscillating at virtually the same frequency (delta frequency

Sirs: Sporadic spastic paraplegia (SSP) and hereditary spastic paraplegia (HSP) are heterogeneous neurodegenerative disorders. On physical examination spasticity of the lower limbs is often predominant, whereas paraparesis may be mild [1, 2]. The gait disorder of SSP/HSP patients which is the cardinal source of disability in these patients has been recently characterized [3]. The treatment of spastic paraplegia is symptomatic and limited to oral antispastic drugs and physiotherapy. In 1984 Penn [4] showed that intrathecal baclofen (ITB) could alleviate spinal cord spasticity. The efficacy of ITB on spasticity has been proven in several studies [5, 6]. In these studies ITB was used as a symptomatic treatment to reduce painful spasm and muscle contractions in mostly wheelchair bound patients. However, SSP/HSP patients are often able to walk even in advanced stages of their disease. Therefore, ITB therapy in SSP/HSP has the special requirement of reducing spasticity but preserving gait function. So far most clinical trials on spasticity rely on rating scales such as the modified “Ashworth Scale of Spasticity” (ASH), which may not adequately reflect the functional benefit in gait in SSP/HSP patients. In the particular case of ITB therapy for SSP/HSP the indication for an ITB pump implantation should moreover be based on the global clinical impression of gait improvement after an ITB test injection. Unfortunately, there are no scientific operational data to test the functional benefit of ITB in SSP/HSP. Here we describe the clinical effect of ITB in 10 patients, who were all treated with oral antispastic drugs and ongoing physiotherapy. Additionally we tested the usefulness of a three-dimensional movement analysis system for the selection of candidates for an ITB pump implantation. The gait of 10 SSP/HSP patients before and after a testing dose of 25 or 50 μg ITB was examined with this method, which is described elsewhere in detail [7]. In cooperation with the responsible physiotherapists we clinically distinguished responders (group 1; n = 5) from non responders (group 2; n = 5) based on the global clinical impression of gait improvement after ITB. Group 1 was recommended for an ITB pump implantation, whereas group 2 was not. With respect to spastic tone SSP/HSP patients showed a significant reduction of the ASH after ITB (p = 0.014). These result are comparable to the study of Penn et al. who analysed the effect of ITB via an implanted pump system [6]. We found an increased gait velocity accompanied by larger step length and a reduced step width after ITB in all patients, but no significant change in other kinematic gait parameters at a self chosen comfortable speed. Additionally, gait analysis was also performed with a fixed velocity of 1 km/h to eliminate the variable influence of speed. Under this condition group 1 presented an increased range of motion (ROM) of the ankle angle. Furthermore group 1 showed a reduction of the minimum knee angle as shown in a patient in Fig. 1. Gait parameters alone, however, did not allow us to separate clinical responders and non responders. An ITB pump implantation was performed in three of the five screened patients of group 1. Two patients did not opt for ITB owing to subjective unsteadiness and weakness in the lower extremities. We were able to collect follow up gait analysis data of two patients under chronic ITB. Both patients showed an effect of chronic ITB (mean dosage 60 μg/day), which was equivalent to the effect of the test bolus (Fig. 2). In conclusion, our findings show that ITB is a potential treatment option in SSP/HSP. However, only 50 % of our patients were recommended for a pump implantation. Therefore it can be assumed that all patients showed a variable effect of ITB that was probably too strong and a formerly existing weakness was unmasked by the ITB in some patients. In the quantitative gait analysis an improvement of gait was documented in the gait velocity and the step length. However, gait analysis alone was not able to discriminate between clinical responders and non-responders. This may be due to the relatively small number of investigated patients. If so, in the individual patient the clinical examination of gait before and after bolus injection of ITB in a multidisciplinary assessment by a neurologist and physiotherapists experienced with gait disorders is decisive and cannot be replaced by a technical assessment alone.

Although gait disturbance is one of the most pronounced and disabling symptoms in cerebellar disease (CD), quantitative studies on this topic are rare.To characterise the typical clinical features of cerebellar gait and to analyse ataxia quantitatively.Twelve patients with various cerebellar disorders were compared with 12 age matched controls. Gait was analysed on a motor driven treadmill using a three dimensional system. A tandem gait paradigm was used to quantify gait ataxia.For normal locomotion, a significantly reduced step frequency with a prolonged stance and double limb support duration was found in patients with CD. All gait measurements were highly variable in CD. Most importantly, balance related gait variables such as step width and foot rotation angles were increased in CD, indicating the need for stability during locomotion. The tandem gait paradigm showed typical features of cerebellar ataxia such as dysmetria, hypometria, hypermetria, and inappropriate timing of foot placement.Typical features of gait in CD are reduced cadence with increased balance related variables and an almost normal range of motion (with increased variability) in the joints of the lower extremity. The tandem gait paradigm accentuates all the features of gait ataxia and is the most sensitive clinical test.

Objective: To evaluate the usefulness of a new instrument for bedside testing of proximal arm and distal finger tapping performance in patients with Parkinson’s disease (PD). Methods: Twenty healthy controls and 25 PD patients with subthalamic nucleus deep brain stimulation were investigated in different treatment conditions using three different tapping paradigms: (1) the standard tapping task of the CAPSIT-PD-protocol; (2) alternate pressing of two buttons on the new board by moving the arm at the elbow and shoulder (proximal tapping), and (3) alternate pressing of two closely collocated buttons on the new board by moving only the index finger (distal tapping) for 30 s. Results: The new tapping board was as sensitive as the standard board to distinguish untreated PD patients from controls. The relative improvements in tapping scores from the off treatment condition were largest for the proximal tapping task. The treatment effects of high frequency stimulation of the subthalamic nucleus or medication alone were comparable, whereas the combined treatment induced significantly higher tapping scores. Conclusion: The new tapping board represents a quick and easy to use bedside test, which may be routinely used to probe the efficacy of treatments on different aspects of motor control.

Deep brain stimulation of the thalamus (thalamic DBS) is an established therapy for medically intractable essential tremor and tremor caused by multiple sclerosis. In both disorders, motor disability results from complex interaction between kinetic tremor and accompanying ataxia with voluntary movements. In clinical studies, the efficacy of thalamic DBS has been thoroughly assessed. However, the optimal anatomical target structure for neurostimulation is still debated and has never been analysed in conjunction with objective measurements of the different aspects of motor impairment. In 10 essential tremor and 11 multiple sclerosis patients, we analysed the effect of thalamic DBS through each contact of the quadripolar electrode on the contralateral tremor rating scale, accelerometry and kinematic measures of reach-to-grasp-movements. These measures were correlated with the anatomical position of the stimulating electrode in stereotactic space and in relation to nuclear boundaries derived from intraoperative microrecording. We found a significant impact of the stereotactic z-coordinate of stimulation contacts on the TRS, accelerometry total power and spatial deviation in the deceleration and target period of reach-to-grasp-movements. Most effective contacts clustered within the subthalamic area (STA) covering the posterior Zona incerta and prelemniscal radiation. Stimulation within this region led to a mean reduction of the lateralized tremor rating scale by 15.8 points which was significantly superior to stimulation within the thalamus (P < 0.05, student's t-test). STA stimulation resulted in reduction of the accelerometry total power by 99%, whereas stimulation at the ventral thalamic border (68%) or within the thalamus proper (2.5%) was significantly less effective (P < 0.01). Concomitantly, STA stimulation led to a significantly higher increase of tremor frequency and decrease in EMG synchronization compared to stimulation within the thalamus proper (P < 0.001). In reach-to-grasp movements, STA stimulation reduced the spatial variability of the movement path in the deceleration period by 28.9% and in the target period by 58.4%, whereas stimulation within the thalamus was again significantly less effective (P < 0.05), with a reduction in the deceleration period between 6.5 and 21.8% and in the target period between 1.2 and 11.3%. An analysis of the nuclear boundaries from intraoperative microrecording confirmed the anatomical impression that most effective electrodes were located within the STA. Our data demonstrate a profound effect of deep brain stimulation of the thalamic region on tremor and ataxia in essential tremor and tremor caused by multiple sclerosis. The better efficacy of stimulation within the STA compared to thalamus proper favours the concept of a modulation of cerebello-thalamic projections underlying the improvement of these symptoms.

Motor outcome following stroke of the internal capsule is variable and its determinants are poorly understood. While many patients fully regain their abilities, recovery of motor functions remains incomplete in others. We analysed functional motor tasks of the upper limb to determine the pattern of focal disability after a small infarct of the internal capsule ('pure motor stroke') in the chronic stage (mean 2.4 years after stroke) with kinematic recordings of a reaching-to-grasp movement, with a quantitative analysis of the precision grip, and with clinical rating scales. The location of the lesions within the posterior limb of the internal capsule (PLIC) in 18 patients was determined from neuroimages obtained in the acute stage (5-20 days after the insult). Involvement of the PLIC was assessed at the level of the basal ganglia, approximately 8 mm above the anterior commissure-posterior commissure level. The distance between the posterior edge of the internal capsule and the centre of gravity of the lesion was determined. Chronic disabilities affected dextrous movements, while paresis was mild and sensitivity for light touch or passive finger flexion was almost normal. For both the reaching-to-grasp movement and the precision grip paradigm, the slowness of movement or force development was confined to the phases when grip formation and stabilization occur, while the onset of hand transport and of the vertical lifting force were not delayed. Grip forces were increased. We observed a close correlation between posterior location within the PLIC and the altered measures of timing and precision grip force. The more posterior the acute lesion was located within the PLIC, the more pronounced were the chronic motor deficits, as seen both in the quantitative measures and in the rating scales. The present study demonstrates for the first time that the amount and quality of chronic motor deficits of dextrous movements are related to a simple measure drawn from routine neuroimaging in the acute stage in patients with capsular stroke. The poor motor outcome in lesions involving the most posterior parts of the PLIC could be due to the condensed organization of corticofugal projections and the density of pyramidal fibres from the primary motor cortex in this subsector. Even small infarcts of this strategic area can disrupt many of the projections from the motor cortices and could thereby limit recovery strategies between homolateral motor representations.

Golge M, Muller M, Dreesmann M, Hoppe B, Wenzelburger R, Kuhtz-Buschbeck JP. Recovery of the precision grip in children after traumatic brain injury. Arch Phys Med Rehabil 2004;85:1435-44. Objective: To identify quantitative parameters that are sensitive enough to detect impairments and improvements of grasping in children after traumatic brain injury (TBI) by analyzing the isometric fingertip forces of a precision grip-lift task. Design: Follow-up and case-control study. Setting: Tertiary pediatric trauma rehabilitation center in Germany. Participants: Thirteen children (age range, 5–14y) with moderate or severe TBI. Trauma severity was assessed with the Glasgow Coma Scale (score range, 3–9) and the Injury Severity Score (range, 16–66 points). Control data were obtained from 13 age- and gender-matched healthy children. Interventions: Not applicable. Main Outcome Measures: Children were examined 3 times (t0, t1, t2). The first date of examination (t0) was defined by the Barthel Index (part B, >20 points). Reexaminations followed after 1 (t1) and 5 (t2) months of inpatient rehabilitation. Quantitative measures included 3 grip-force parameters, 2 load force parameters, 1 parameter of the coordination between grip force and load force, and 3 timing parameters in a precision grip-lift task. Clinical improvements and recovery of activities of daily living were described with the Barthel Index (qualitative measure). Results: Peak grip force, maximum negative load force, grip force in the static phase and its standard deviation, and grip-force/load-force ratio at maximum grip force showed significant improvements during the observation period (5mo). Also, the preparation phase and preload duration, but not the load duration, changed significantly. Conclusions: Impairments and the recovery of grasping in children after TBI can be objectified with quantitative analyses of the precision grip. Several grip-force and timing parameters were sensitive for the description of restitution processes.

Experimental and clinical data indicate that the cerebellum is involved in the pathophysiology of advanced stages of essential tremor (ET). The aim of this study was to determine whether a dysfunction also affects cerebellar structures involved in eye movement control. Eye movements of 14 patients with ET and 11 age-matched control subjects were recorded using the scleral search-coil technique. Vestibular function was assessed by electro-oculography. Eight ET patients had clinical evidence of intention tremor (ET(IT)); six had a predominantly postural tremor (ET(PT)) without intention tremor. ET patients showed two major deficits that may indicate cerebellar dysfunction: (i) an impaired smooth pursuit initiation; and (ii) pathological suppression of the vestibulo-ocular reflex (VOR) time constant by head tilts ('otolith dumping'). In the step ramp smooth pursuit paradigm, the initial eye acceleration in the first 60 ms of pursuit generation was significantly reduced in ET patients, particularly in ET(IT) patients, by approximately 44% (mean 23.4 degrees/s(2)) compared with that of control subjects (mean 41.3 degrees/s(2)). Subsequent steady-state pursuit velocity and sinusoidal pursuit gain (e.g. 0.4 Hz: 0.90 versus 0.78) were also significantly decreased in ET patients, whereas pursuit latency was unaffected. The intention tremor score correlated with the pursuit deficit, e.g. ET(IT) patients were significantly more affected than ET(PT) patients. Gain and time constant (tau) of horizontal VOR were normal, but suppression of the VOR time constant by head tilt ('otolith dumping') was pathological in 41% of ET patients, particularly in ET(IT) patients. Saccades and gaze-holding function were not impaired. The deficit of pursuit initiation, its correlation with the intensity of intention tremor, and the pathological VOR dumping provide additional evidence of a cerebellar dysfunction in the advanced stage of ET, when intention tremor becomes part of the clinical symptoms, and point to a common pathomechanism. The oculomotor deficits may indicate an impairment of the caudal vermis in ET.

The aim of this study was to characterize impairments of hand function in individuals with myelomeningocele (MMC) using a quantitative method. A grip-lift task was studied in 29 individuals with MMC (17 females, 12 males; mean age 12 years 4 months, SD 5 years 6 months; range 4 to 28 years) and 29 age- and sex-matched control participants. A small object (weight 200 g) was grasped and lifted with a precision grip of the dominant hand and grip forces (GF) and time intervals were measured. Sensibility was examined with a two-point discrimination test. In those with MMC, the latency between GF onset of the thumb and index finger and ensuing preload duration were both significantly prolonged (p

We assessed force coordination of the hand in Parkinson's disease and its relationship to motor complications of levodopa therapy, particularly to levodopa-induced dyskinesias (LID). We studied two groups of Parkinson's disease patients with (Parkinson's disease + LID, n = 23) and without levodopa-induced dyskinesias (Parkinson's disease - LID, n = 10), and age-matched healthy controls. The motor score of the Unified Parkinson's Disease Rating Scale, a dyskinesia score and force in a grip-lift paradigm were assessed ON and OFF levodopa. A pathological increase of forces was seen in ON-state in Parkinson's disease + LID only. In Parkinson's disease + LID, the force involved in pressing down the object before lifting was significantly increased by levodopa (by 61%, P < 0.05). An overshooting of peak grip force by 51% (P < 0.05) and of static grip force by 45% (P < 0.01) was observed in the ON- compared with the OFF-drug condition. In contrast, no excessive force was found in Parkinson's disease - LID. Peak grip force in ON-state was 140% (P < 0.05) higher in Parkinson's disease + LID than in Parkinson's disease - LID, while static grip force was increased by 138% (P < 0.01) between groups. Severity of peak-dose dyskinesias was strongly correlated with grip force in ON-state (r = 0.79 with peak force, P < 0.01). No correlation was observed between forces and the motor score as well as with the daily dose of dopaminergic medication. Force excess was only observed in patients with LID and motor fluctuations. A close relationship was seen between the overshooting of forces and dyskinesias in the ON-drug condition. We postulate that both LID and grip force excess share common pathophysiological mechanisms related to motor fluctuations.

Gait analysis was carried out to assess the effects of L-dopa and bilateral subthalamic nucleus stimulation on gait velocity, cadence, stride length, and gait kinematics in nine patients with PD. Substantial effects of bilateral subthalamic nucleus stimulation on gait, with an increase in gait velocity and stride length comparable to that of a suprathreshold L-dopa dose, were found. Interestingly, stride length was more improved by L-dopa and cadence more by subthalamic nucleus stimulation. In two patients with freezing during the "on" period, subthalamic nucleus stimulation failed to reduce this symptom effectively.

OBJECTIVES Postural tremor is a regularly encountered side effect of amitriptyline which can be strong enough to cause discontinuation of therapy. The aim was to characterise amitriptyline induced tremor and to assess if the central or reflex component of physiological tremor was modulated by this drug. METHODS The postural hand tremor was measured in 15 patients on a clinical rating scale, by power spectral analysis of accelerometer, forearm flexor, and extensor EMG before and after the beginning of amitriptyline treatment for major depression or chronic pain syndrome. A coherence analysis between flexor and extensor muscles on the same side was performed. RESULTS There was a clinically visible increase in postural tremor in a third of these patients. The tremor amplitude measured by accelerometer total power increased in every patient under amitriptyline. The EMG synchronisation as reflected by significant peaks in the flexor or extensor spectrum generally occurring at higher frequencies (8–18 Hz) than the accelerometric tremor frequencies (6–11 Hz) did not change. The number of patients with a significant flexor-extensor coherence in the 7–15 Hz range increased significantly under amitriptyline, the frequency bands of significant coherence corresponded with the EMG frequencies, and both were independent of changes to the hand9s resonant frequency by added inertia. CONCLUSIONS An enhancement of postural tremor under amitriptyline is a common phenomenon although not always clinically apparent. The increase in EMG-EMG coherence indicates an increased common central drive to the motor units as its frequency is not influenced by peripheral resonance or reflex mechanisms. This is the first account of a drug induced enhancement of the central component of physiological tremor.

The aim of this study was to quantify the tremor of the hand during a natural movement (kinetic tremor) in tremor-dominant parkinsonian patients (n = 13). We used a three-dimensional camera system to kinematically analyze rest and kinetic tremors in an unrestrained reach-to-grasp movement, and additional tremor recordings were performed under standard postural and rest conditions using electromyography and accelerometry. The standard analysis showed a highly synchronized tremor with similar frequencies at rest and in sustained postural tasks, with and without loading. A kinematic recording was used to compare rest and action conditions. A strong inhibition of the resting tremor was present at the onset of the movement and reached its peak during deceleration. A kinetic tremor of low amplitude was present in most of the parkinsonian patients, but its occurrence was confined mainly to the terminal periods of the movement. The frequency of kinetic tremor was significantly higher than that at rest, before the onset of the movement in Parkinson's disease, as determined by the kinematic analysis (mean, 5.5 Hz vs 6.5 Hz; p0.01). Our results confirm similarities between the tremor at rest and the oscillations during a sustained postural task in classic parkinsonian tremor. In contrast to this stable tremor, which seems to be generated by basal ganglia oscillators, a different pathophysiology of oscillations during motion must be considered. The kinetic tremor is most likely related to an enhancement of the physiologic tremor in the terminal phase of the reach-to-grasp movement.

The cerebellum is assumed to play a major role in the pathophysiology of essential tremor (ET). As intention tremor is considered one of the classical features of cerebellar disease, we have assessed a large group of patients with ET for the semiology of the tremor and have performed objective quantitative analysis of a grasping movement in patients with ET, cerebellar disease and a normal control group. We found 25% of the patients to have a moderate or severe kinetic tremor with clear-cut features of a classical intention tremor. Another 33% of the patients had a mild intentional component of their kinetic tremor. Patients with intention tremor (ET(IT)) did not differ from those with predominant postural tremor (ET(PT)) with respect to alcohol sensitivity of the tremor and the frequency of a family history. ET(IT) patients were older and more often showed head and trunk involvement. The onset of this intention tremor has been assessed retrospectively. It was found to begin at a randomly distributed time interval after the onset of the postural tremor, but older patients had a shorter time to development of intention tremor. Quantitative accelerometry of postural tremor showed similar tremor frequencies in both patient groups, but ET(IT) patients had a slightly larger tremor amplitude. Quantitative analysis of a grasping movement using an infrared-camera system was performed in two subgroups of the patients with ET(PT) and ET(IT) and control groups with cerebellar disease or normal subjects. The intention tremor could be quantified objectively as an increased amplitude of curvature during the deceleration and target phase of the movement. The amplitude measurements of intention tremor were clearly abnormal and of comparable magnitude for ET(PT) and cerebellar disease. Additionally, the patients with ET(IT) had a significantly slowed grasping movement during the deceleration and target period. Hypermetria was significantly increased for the patients with ET(IT) and cerebellar disease. We conclude that intention tremor is a feature of ET. ET(IT) patients have abnormalities of their upper limb function compatible with cerebellar disease. This suggests that patients with more advanced ET show abnormalities of cerebellar functions.