Does tremor pace repetitive voluntary motor behavior in parkinson's disease?

In patients with Parkinson's disease and in normal subjects, the influence of tremor on repetitive voluntary movement was investigated in the index finger by comparing frequency of isometric force tremor with frequency of voluntary alternating isometric contractions. Tremor frequency, measured over the range from 0 to 70% maximum voluntary force, usually increased with force. The tremor frequency band was lower and more often overlapped with the upper voluntary frequency range in patients than in normal subjects. Normal subjects could accurately produce voluntary contractions at all cue frequencies from 1 to 5 Hz. Patients could produce auditory-paced frequencies of 1 and 2 Hz, but at higher cue frequencies, their voluntary contractions were often faster or slower than the cue. The faster or "hastened" voluntary frequencies were within the tremor frequency band, whereas the slowed voluntary frequencies were below it. Maximal voluntary frequency was often greater than the lowest but always less than the highest tremor frequency. It is concluded that parkinsonian tremor may pace voluntary repetitive movements to go faster than intended with the highest tremor frequency being an upper limit for voluntary frequency. Similar mechanisms may underlie the hastened repetitive vocal responses that were also observed in the parkinsonian patients.     

Sensory processing during kinesthetic aftereffect following illusory hand movement elicited by tendon vibration

We investigated how the human sensory-motor system elicits a somatosensory aftereffect. Tendon vibration of a limb excites the muscle spindle afferents that contribute to eliciting illusory movements of the limb. After the cessation of vibration, a transient sensation in which the vibrated limb returns towards its original position (kinesthetic aftereffect) is often experienced, even in the absence of the afferent inputs recruited by the vibration. We vibrated the tendon of either the right wrist extensor or flexor muscle that elicited an illusory flexion or extension movement, which was followed by its corresponding extension or flexion aftereffect. First, we psychophysically investigated how the preceding illusory movement affects the aftereffect. Second, we examined the cortico-spinal excitability during the aftereffect to evaluate its changes from the time during the illusion. We measured the amplitude of the motor-evoked potential that is evoked by a single-pulse transcranial magnetic stimulation to the hand section of the contralateral motor cortex (M1). All 19 subjects experienced the aftereffect, and the amount of aftereffect was approximately 70% of the preceding illusion. During the illusion, the cortico-spinal excitability increased more in non-vibrated than in vibrated muscle, so as to reflect the illusory directions. During the aftereffect, the excitability was significantly reduced only in the non-vibrated muscle, with no change in the vibrated muscle, which, in turn, caused an opposite pattern in the unbalanced excitability between the two muscles, and the degree of unbalanced excitability was correlated with the sensation of aftereffect. The kinesthetic aftereffect seems to be elicited by a sensory process that is determined by the preceding illusory movements. Motor-cortical processing of the unbalanced sensory information from the stimulated and non-stimulated muscles may contribute to the elicitation of kinesthetic aftereffect.     

Characteristics of parkinsonian and ataxic gaits: a study using surface electromyograms, angular displacements and floor reaction forces

To clarify the characteristics of parkinsonian and ataxic gaits, we analyzed electromyograms (EMGs) of the thigh and leg muscles, angular displacements of the hip and leg joints, and floor reaction forces during free walking for each gait phase in 16 patients with Parkinson's disease (PD) and 14 ataxic patients with cerebellar degenerations. We studied 17 healthy elderly subjects whose walking speed was similar to that of patients with moderate disease. Free walking by PD patients was characterized by low maximum activity of the gastrocnemius/soleus (GC) and tibialis anterior (TA) muscles. Ataxic patients showed high activity of GC and TA during the period when these muscles were not active in normal walking. The ratio of changes of EMG of the distal muscles to changes in angular displacement of the ankle (DeltaEMG/Deltaangle) was reduced in GC of PD patients in ankle dorsiflexion, whereas it was high in GC and TA of ataxic patients in ankle dorsiflexion and plantarflexion, respectively. Changes in DeltaEMG/Deltaangle coincided with those in proprioceptive reflexes reported previously. Our results showed that measurement of EMG for each phase revealed disease-specific factors, and that of DeltaEMG/Deltaangle might be a conventional clue for estimation of reflexes for these gait disorders.     

Reaction time and movement velocity abnormalities in Parkinson's disease under different task conditions

We examined reaction times, movement velocities, and the associated agonist and antagonist muscle behaviors in nine Parkinson's disease (PD) patients and eight normal subjects before and after medications, using a wrist extension task to changing locations of a visual target. Targets changing 500 msec before an auditory "go" signal act as a preparatory cue, while targets changing at the time of the go signal provide a combined auditory and visual stimulus. Late target changes allowed examination of (1) reaction times during an ongoing movement, and (2) movement in the presence and absence of visual targets. PD prolonged the time from the onset agonist electromyographic activity and reduction of antagonist activity to movement onset. Both were shortened by preparatory cues and combined visual and auditory go signals. PD slowed movement only in a subset of trials in which there was movement to a displayed target.     

Deficits in reciprocal inhibition of children with cerebral palsy as revealed by H reflex testing

Experiments were performed to determine whether spinal and supraspinal components of reciprocal inhibition (a neural mechanism responsible for the prevention of muscular co-ordination during voluntary movement) were present in groups of non-disabled children and children with cerebral palsy. Changes in the gastrocnemius-soleus H reflex were examined during voluntary dorsiflexion and plantarflexion of the ankle and during a vibration applied to the anterior tibial tendon. The results indicate that children with cerebral palsy have impairments in reciprocal inhibition, both before and during voluntary movement. These deficits, which involve damage to supraspinal centres, contribute to their inability to perform smooth, co-ordinated movements.     

Jaw movement dysfunction related to Parkinson's disease and partially modified by levodopa.

OBJECTIVES--To test the hypotheses that Parkinson's disease can differentially produce deficits in voluntary and rhythmic jaw movements, which involve different neuronal circuits, and that levodopa treatment improves specific components of the motor deficit. METHODS--Patients with idiopathic Parkinson's disease and control subjects were tested on a series of jaw motor tasks that included simple voluntary movement, isometric clenching, and natural and paced rhythmic movements. Jaw movements were measured by changes in electromagnetic fields and EMG activity. Patients with Parkinson's disease with fluctuations in motor responses to levodopa were tested while off and on. RESULTS--During the off state, patients with Parkinson's disease were significantly worse than the control subjects on most tasks. The deficits included a decrease in amplitude and velocity during jaw opening and closing, aberrant patterns and low amplitude of EMG activity during clenching, and low vertical amplitude and prolonged durations of occlusion during rhythmic movements. No decrements were found in the amplitude of voluntary lateral jaw movements or the frequency of rhythmic movements. During the on state, improvements occurred in the patterns and level of EMG activity during clenching and in the vertical amplitude and duration of occlusion during rhythmic movements, although a significant decrement occurred in the lateral excursion of the jaw. CONCLUSIONS--Parkinson's disease affects the central programming of functionally related muscles involved in voluntary and rhythmic jaw movements and levodopa replacement influences only certain aspects of jaw movement, most likely those requiring sensory feedback.     

A startling acoustic stimulus facilitates voluntary lower extremity movements and automatic postural responses in people with chronic stroke

A startling acoustic stimulus (SAS) involuntary releases prepared movements at accelerated latencies, known as the StartReact effect. Previous work has demonstrated intact StartReact in paretic upper extremity movements in people after stroke, suggesting preserved motor preparation. The question remains whether motor preparation of lower extremity movements is also unaffected after stroke. Here, we investigated StartReact effects on ballistic lower extremity movements and on automatic postural responses (APRs) following perturbations to standing balance. These APRs are particularly interesting as they are critical to prevent a fall following balance perturbations, but show substantial delays and poor muscle coordination after stroke. Twelve chronic stroke patients and 12 healthy controls performed voluntary ankle dorsiflexion movements in response to a visual stimulus, and responded to backward balance perturbations evoking APRs. Twenty-five percent of all trials contained a SAS (120 dB) simultaneously with the visual stimulus or balance perturbation. As expected, in the absence of a SAS muscle and movement onset latencies at the paretic side were delayed compared to the non-paretic leg and to controls. The SAS accelerated ankle dorsiflexion onsets in both the legs of the stroke subjects and in controls. Following perturbations, the SAS accelerated bilateral APR onsets not only in controls, but for the first time, we also demonstrated this effect in people after stroke. Moreover, APR inter- and intra-limb muscle coordination was rather weak in our stroke subjects, but substantially improved when the SAS was applied. These findings show preserved movement preparation, suggesting that there is residual (subcortical) capacity for motor recovery.     

Flexor reflexes in chronic spinal cord injury triggered by imposed ankle rotation

Hypersensitivity of the flexor reflexes to input from force-sensitive muscle afferents may contribute to the prevalence and severity of muscle spasms in patients with spinal cord injuries. In the present study, we triggered flexor reflexes with constant-velocity ankle movements into end-range dorsiflexion and plantarflexion positions in 8 individuals with spinal cord injuries. We found that all 8 subjects had coordinated increases in flexion torque at the hip and ankle following externally imposed plantarflexion movements at the ankle. In addition, end-range dorsiflexion movements also triggered flexor reflexes in 3 subjects, although greater loads were required to trigger such reflexes using dorsiflexion movements (compared to plantarflexion movements). These three-joint reflex torque patterns triggered by ankle movement were broadly comparable to flexion withdrawal responses elicited by electrocutaneous stimuli applied to a toe, although the amplitude of the torque response was generally lower. We conclude that excitation of muscle and joint-related afferents induced by end-range movements may be responsible for exaggerated flexion reflex responses in spinal cord injury.     

Ankle dexterity is less impaired than muscle strength in incomplete spinal cord lesion

Background Motor assessment after incomplete spinal cord injury (iSCI) currently consists of tests for muscle strength (manual muscle testing) and gait. The ability to adequately time a movement, an aspect of dexterity, is not tested. Thus, this study assessed the timing of ankle dorsiflexion in iSCI patients in the supine position and during gait and examined its relation to measures for muscle strength, corticospinal conductivity and gait speed. Methods In 12 subjects with iSCI and 12 matched controls, timing of ankle dorsiflexion was tested by means of auditory-paced dorsiand plantar-flexion movements at three frequencies in the supine position and by determining initiation and termination of dorsiflexion in swing during gait. In addition, maximal movement velocity (MMV) in the ankle task, maximal voluntary contraction (MVC), corticospinal conductivity (motor evoked potentials (MEP)) and gait speed (10 Meter Walk Test) were assessed. Results The groups did not significantly differ in timing of ankle dorsiflexion, neither in the supine position nor in gait. However, they significantly differed in MMV at all frequencies, MEP latency, MEP amplitude and gait speed. In contrast to ankle timing in the supine position, the onset of dorsiflexion in swing during gait significantly correlated to the dynamic MEP parameters. Conclusions Although MMV and gait speed were significantly reduced, timing of ankle dorsiflexion, both in the supine position and during gait,was less impaired in iSCI patients. This indicates that the loss of strength, particularly of dynamic strength, is the major motor impairment in iSCI, which might be considered when assessing treatment interventions.     

Axial versus distal motor impairment in Parkinson's disease

We measured axial (head rotation) and distal (wrist flexion and extension) movements in parkinsonian patients with varying stages of disability, before and after administration of L-dopa. Velocities for both movements were proportionately reduced in all stages of disease. L-Dopa administration provided a small but consistent increase in distal movement velocity for most patients, whereas in patients with advanced disease (stages III to V), axial movement velocity actually declined after administration of L-dopa. This decline may be partially responsible for the failure of L-dopa administration to reverse the loss of "righting reflexes" in these patients. Measurement of axial motor control may be a useful tool in evaluating therapeutics for Parkinson's disease patients.     

Hypokinesia of associated movement in Parkinson's disease: A symptom in early stages of the disease

We compared the degrees of impairment between intended voluntary movement and its simultaneous automatic associated movement in Parkinson's disease (PD). We studied wrist dorsiflexion as a movement associated with grip in 20 patients with PD and in 20 normal controls. The patients showed a significantly smaller dorsiflexion as compared with the controls. The decrease in associated movement was related to the severity of clinical stage of the disease, while gripping was performed well in each stage. The temporal relationship between grip and associated movement was the same for both groups of subjects. The patients showed no disturbance of amplitude or velocity for a single motor act of wrist dorsiflexion. Persons with PD have a greater reduction of automatic associated movement than intended voluntary movement. This may be one of the bases of clinical symptoms of PD patients in early stages of the disease.     

Reaction times of movement preparation in patients with Parkinson's disease

We studied the onset of preparatory postural responses and subsequent voluntary movements by measuring soleus muscle activities in the standing position in 20 patients with Parkinson's disease. We measured the postural response in preparing to rise on tiptoe as the onset of the premotion silent period (PMSP). Our patients showed no delay when compared with age-matched healthy controls, but did show a significant delay in the onset of voluntary movement. The elongated PMSP (increased duration of the preparatory postural adjustments) was related to the severity of bradykinesia. Results indicate that the conventional reaction time is increased in patients with Parkinson's disease, even though there is no delay of central processing for the preparation of voluntary movements, and that there is bradykinesia of involuntary postural movements.     

Movement perception of the tonic vibration reflex is abnormal in functional limb weakness

IntroductionWe tested the hypothesis that functional limb weakness is associated with possible dysfunction of the central processing of proprioceptive information, by evaluating the amount of tonic vibration reflex (TVR) and the perception of the TVR movement.MethodsThe study sample was 20 patients with functional weakness of the lower and/or the upper limbs and 25 healthy controls; delivery of 92-Hz transcutaneous vibration of the biceps brachii tendon of the unrestrained arm stimulated predominantly the muscle spindle afferent and elicited elbow flexion (tonic vibration reflex, TVR). Blindfolded participants had to match the final position of the vibrated arm with their contralateral tracking arm. The TVR and perception of the TVR movement were measured as angle movements of the vibrated arm and the tracking arm, respectively.ResultsThe magnitude of the TVR of the vibrated arm and movement perception of the TVR of the tracking arm were significantly reduced in the patients compared to the controls. No correlation was found between magnitude of the TVR and perception of the TVR movement, suggesting that the abnormalities were independent of each other. Moreover, the abnormalities did not differ between the patients with/without bilateral upper limb involvement or between the affected and the unaffected side in patients with unilateral impairment, suggesting that the observed deficits are independent of motor impairment.ConclusionsProprioceptive dysfunction may underlie alterations in body movement and in sense of agency in such patients and may play a role in the pathophysiology of functional limb weakness.     

The role of language areas in motor control dysfunction in Parkinson's disease

We evaluated the differences in motor control organization between parkinsonian patients with (seven cases) and without (ten cases) gait disorder. We used positron emission tomography (O¹⁵-H₂O-PET) to measure regional cerebral blood flow as a correlate for local neuronal activation. This has been assessed during repetitive joystick movements of the right hand, externally triggered using a metronome as an auditory cue. In patients with Parkinson's disease (PD) without gait disorder, the contralateral supplementary motor cortex and the bilateral cerebellum were activated while in PD patients with gait disorder the contralateral Broca's area, the contralateral sensory motor cortex and the homolateral cerebellum were activated. Our results suggest that PD patients with gait disorder creates an internal verbal cue in order to control the output of the movement of joystick, supplying the loss of control of the supplementary motor cortex that is activated in patients without gait disorder.     

Ballistic and corrective movements on an aiming task. Intention tremor and parkinsonian movement disorders compared.

Six patients with Parkinson's disease, six patients with essential or intention tremor, and nine controls were tested on a step-tracking task using a joystick control and oscilloscope display. Tremor subjects resembled controls in making an initial ballistic movement followed by (defective) corrections, and took longer than the controls to reach the target with small amplitude jumps, but not with larger ones. The reverse was true for parkinsonian subjects, who acquired the target with slow corrective movements only. This suggests that two kinds of movement available to normal people are selectively impaired in these disorders; ballistic movements in Parkinson's disease and small amplitude corrective movements in the other disorders.     

Switching of movement direction is central to parkinsonian bradykinesia in sit-to-stand.

Patients with Parkinson's disease (PD) are known to manifest slowness in movements. We sought to identify the particular kinematic and kinetic disorders that contribute to the slowness in performing sit-to-stand in these patients. Two inter-related studies were carried out. In the first study, 20 patients with PD and 20 control subjects were instructed to perform sit-to-stand at a natural speed. In the second study, 15 control subjects were instructed to simulate the slower speed of sit-to-stand of the patients identified in the first study. Kinematic and kinetic data were recorded by a PEAK motion analysis system and two force platforms. The results showed that patients with PD generated smaller peak horizontal and vertical velocities during the task. They took a longer time to complete each individual phase as well as the whole movement of sit-to-stand. Patients also produced smaller peak hip flexion and ankle dorsiflexion joint torques and had prolonged time-to-peak torques from sit-to-stand onset. When control subjects simulated the patients' speed of sit-to-stand, there was no difference in all the kinematic and kinetic data between groups. The only exception was that they exhibited a shorter transition time between peak horizontal velocity (flexion phase) and seat-off (extension phase) than the patients. This study demonstrated that the slowness of PD patients during sit-to-stand at a natural speed could be attributed to inadequate peak hip flexion and ankle dorsiflexion torques, a prolonged torque production, as well as a difficulty in switching from the flexion to extension direction during sit-to-stand. As the latter difficulty persisted when the control subjects performed the task at a speed similar to that of the patients, our findings suggest that a fundamental problem of patients with Parkinson's disease could be a switch between movement directions.     

Whipple's disease mimicking progressive supranuclear palsy: the diagnostic value of eye movement recording

Treatable causes of parkinsonian syndromes are rare; Whipple's disease is one of them. A patient is described who presented with a parkinsonian syndrome and abnormal vertical gaze. Measurement of eye movements showed marked slowing of upward saccades, moderate slowing of downward saccades, a full range of voluntary vertical eye movements, curved trajectories of oblique saccades, and absence of square wave jerks. These features, atypical of progressive supranuclear palsy, suggested the diagnosis of Whipple's disease, which was subsequently confirmed by polymerase chain reaction analysis of intestinal biopsy material. Precise measurement of the dynamic properties of saccadic eye movements in parkinsonian patients may provide a means of identifying treatable disorders.     

Parkinsonian arm movements as altered by task difficulty

A discrete elbow movement to targets with different indexes of difficulty (ID) was used to determine the kinematic organization of arm movements in a young, an elderly and a Parkinson's disease (PD) group (n = 14). Target size and movement amplitude changes led to expected modifications of the kinematics in all three groups according to Fitts' law. Increased task demands by changing target size produced not only differences between the age-groups, but affected the modulation of velocity and acceleration in the parkinsonian patients differentially. For large amplitude movements, the PD patients were less able to increase velocity and acceleration magnitudes when target accuracy constraints were reduced. These findings, when taken together with the observation that speed scaling was preserved for small movement amplitudes, suggest that a reduced capability to initiate and regulate force is the cause for the observed slowness in PD.     

The effect of ankle joint position and effort on quadriceps reflex sensitivity.

OBJECTIVE: To investigate a possible ankle-knee synergy, experiments with normal subjects were performed to compare changes of the quadriceps motor pool excitability due to ankle position and effort. METHODS: Vastus medialis H reflex amplitude was examined during ankle isometric contractions conditioned by different ankle positions (dorsiflexion, neutral, and plantarfiexion) with or without voluntary effort (either in the dorsiflexion or plantarflexion direction). Repeated measures ANOVAs were performed on the mean and standard deviation of the H peak-to-peak amplitude. RESULTS: Mean vastus medialis H reflex amplitudes were significantly different among the trials of different ankle efforts (P<0.05), and significantly increased during plantarfiexion efforts. In contrast, mean vastus medialis H reflex amplitude did not vary with respect to changes of ankle position (P>0.05). CONCLUSIONS: The data suggest that (1) the position of the ankle joint did not significantly modify the excitability of the neuromotor pool of the VM muscle, in either static or active cases, and (2) the effort effect from the ankle joint on the VM neuromotor pool is most significant during ankle plantarfiexion effort. Possible mechanisms are central motor irradiation and peripheral force-dependent pathways from the ankle joint that influence the VM neuromotor pool.     

Disruption of spatial organization and interjoint coordination in Parkinson's disease, progressive supranuclear palsy, and multiple system atrophy.

Patients with basal ganglia diseases may exhibit ideomotor apraxia. To define the nature of the impairment of the action production system, we studied a repetitive gesture of slicing bread by three-dimensional computergraphic analysis in eight nondemented patients with Parkinson's disease in the "on" state, five with progressive supranuclear palsy and four with multiple system atrophy. Two patients with Parkinson's disease and two with progressive supranuclear palsy showed ideomotor apraxia for transitive movements on standard testing. A Selspott II system was used for kinematic analysis of wrist trajectories and angular motions of the shoulder and elbow joints. Patients with Parkinson's disease, progressive supranuclear palsy, and even some with multiple system atrophy exhibited kinematic deficits in the spatial precision of movement and velocity-curvature relationships; in addition, they failed to maintain proper angle/angle relationships and to apportion their relative joint amplitudes normally. Spatial disruption of wrist trajectories was more severe in patients with ideomotor apraxia. We posit that the basal ganglia are part of the parallel parieto-frontal circuits devoted to sensorimotor integration for object-oriented behavior. The severity and characteristics of spatial abnormalities of a transitive movement would therefore depend on the location and distribution of the pathologic process within these circuits.