Step-tracking movements of the wrist in humans. I. Kinematic analysis

We have examined the kinematics of the initial trajectory of step-tracking movements performed by human subjects. Each subject tracked a target that required 5-30 degrees of radial or ulnar deviation of the wrist. All movements were to be performed as accurately as possible. Speed instructions were given before each trial. When subjects performed different amplitude movements following the same speed instruction, the peaks of velocity, acceleration, and jerk were linearly related to peak displacement. The peaks of velocity, acceleration, and jerk also changed when the speed instruction was altered. Thus, for any given movement, the peak values of the derivatives of displacement were dependent on both movement amplitude and intended speed. As a result, the peak values of the derivatives cannot be used by themselves to control or monitor peak displacement. When subjects performed different amplitude movements following the same speed instruction, movement duration tended to remain constant. In contrast, movement duration changed when the speed instruction was altered. Movements performed when subjects intended to move slowly had longer durations than when subjects intended to move quickly. These results suggest that subjects volitionally alter intended speed by selecting different movement durations. When both movement amplitude and intended speed were varied, the peak displacement of a step-tracking movement was linearly related to the product of 2 kinematic variables: the initial peak of a derivative of displacement (either velocity, acceleration, or jerk) and movement duration. On the basis of our observations, we propose that central commands generate step-tracking movements of different amplitudes and intended speeds by adjusting both the magnitude and duration of a derivative of displacement.     

A loss of a velocity‐duration trade‐off impairs movement precision in patients with cerebellar degeneration

Current theories discussing the role of the cerebellum have been consistently pointing towards the concept of motor learning. The unavailability of a structure for motor learning able to use information on past errors to change future movements should cause consistent metrical deviations and an inability to correct them; however, it should not boost “motor noise.” However, dysmetria, a loss of endpoint precision and an increase in endpoint variability (“motor noise”) of goal‐directed movements is the central aspect of cerebellar ataxia. Does the prevention of dysmetria or “motor noise” by the healthy cerebellum tell us anything about its normal function? We hypothesize that the healthy cerebellum is able to prevent dysmetria by adjusting movement duration such as to compensate changes in movement velocity. To address this question, we studied fast goal‐directed index finger movements in patients with global cerebellar degeneration and in healthy subjects. We demonstrate that healthy subjects are able to maintain endpoint precision despite continuous fluctuations in movement velocity because they are able to adjust the overall movement duration in a fully compensatory manner (“velocity‐duration trade‐off”). We furthermore provide evidence that this velocity‐duration trade‐off accommodated by the healthy cerebellum is based on a priori information on the future movement velocity. This ability is lost in cerebellar disease. We suggest that the dysmetria observed in cerebellar patients is a direct consequence of the loss of a cerebellum‐based velocity‐duration trade‐off mechanism that continuously fine‐tunes movement durations using information on the expected velocity of the upcoming movement.     

Fast voluntary neck movements in patients with cervical dystonia: a kinematic study before and after therapy with botulinum toxin type A.

OBJECTIVE: To study fast voluntary neck movements in patients with cervical dystonia (CD) before and after therapy with botulinum toxin type-A (BTX-A). METHODS: A selected sample of 15 patients with CD (with prevalent torticollis) and 13 age-matched control subjects performed both right and left rotational, and flexion and extension neck movements as fast as possible. Movements were recorded with a motion analysis system (SMART, BTS). Movement time, angular amplitude, and peak angular velocity were analyzed. In patients, rotational neck movements were pooled as "pro-dystonic" (toward the dystonic side) and "anti-dystonic" (toward the non-dystonic side). Results obtained in patients before BTX-A treatment were compared with those of control subjects. The effect of BTX-A treatment was evaluated by comparing movement performance before and after treatment. RESULTS: Before receiving BTX-A, patients performed pro- and anti-dystonic movements with lower peak angular velocity than control subjects. Pro-dystonic movements had a reduced angular amplitude. Anti-dystonic movements showed an abnormally long movement time. Flexion and extension movements required longer movement times, but the other kinematic variables were normal. After BTX-A injections, pro-dystonic movement amplitude and anti-dystonic movement peak angular velocity increased, whereas flexion and extension movements remained unchanged. CONCLUSIONS: Before BTX-A injection patients with CD perform fast voluntary neck movements abnormally and BTX-A injections improved their peak velocity and amplitude. SIGNIFICANCE: Kinematic studies can detect specific neck movement disturbance in patients with CD, and can quantify both the severity of clinical picture and the effect of BTX-A injections in these patients.     

Temporal movement control in patients with Parkinson''s disease.

Patients with Parkinson's disease (PD) have been reported to be unable to modify their movement velocity to adapt to changing environmental demands. For example, when movement amplitude is varied, PD patients usually exhibit a nearly constant peak velocity, whereas elderly subjects show an increase of their peak velocity with increased amplitude. The experiment examined the ability of PD patients to vary the duration of their movement (four different percentages of their maximum) under conditions where temporal, but not spatial, control was emphasised. PD patients had longer movement times than control subjects, but were able to vary the duration of their movement with comparable temporal accuracy to that of elderly subjects. For both groups, the agonist EMG activity increased with decreased movement duration. For the PD patients, the number of agonist bursts increased with increased movement duration.     

Effects of expected perturbations on the velocity control of fast arm abduction movements

A triphasic electromyographic pattern of sequential activation of agonist, antagonist, and again agonist muscles underlies rapid or ballistic limb movements in humans. The first agonist burst reflects muscular force accelerating the limb, the antagonist burst is mainly related to the braking process of movement, while the second agonist burst is considered a reactive adjustment to the deceleration. The duration of the first agonist burst has been reported to be constant for movements of different amplitudes, thus suggesting that only changes in its amplitude contribute to the velocity control of movement. The present research has been undertaken to investigate the strategy whereby the nervous system increases agonist impulsive force for ballistic performance in response to experimental conditions requiring perceptual and/or provisional processes related to expected changes in load or accuracy constraints. The effects of expected perturbations of different strengths on some kinematic and electromyographic variables of fast arm abduction movements performed in a step-tracking task and in an outer-stop terminated task were analyzed in normal subjects. All motor performances were characterized by triphasic electromyographic patterns. In the absence of expected perturbations, the mean velocity of the movements was markedly higher in the outer-stop terminated task. Correspondingly, greater amplitudes and durations of the first agonist burst were observed. In both types of motor tasks, when expected perturbations were inserted, the velocity of the movement increased as well as the amplitude and the duration of the first agonist burst. These results, in agreement with previous observations, indicate that the normal mechanism, whereby the nervous system increases agonist impulsive force in rapid movements, comprises changes not only in the amplitude but also in the duration of the first agonist burst.     

Voluntary movement at the elbow in spastic hemiparesis

The relative importance of hyperreflexia and paresis in disturbances of voluntary arm movement was studied in a group of patients (n = 25) with spasticity arising from a unilateral ischemic cerebral lesion. Patient performance was evaluated against data obtained from normal subjects (n = 15). Spastic patients achieved lower maximum movement velocities during flexion or extension than did normal subjects. The more marked the paresis of the elbow flexor and extensor muscles of the patients, relative to the strength of the normal subjects, the greater was this reduction in maximum velocity. For a given velocity, however, the time taken to complete a movement and the time to reach the peak velocity were normal. No relationship was found between the degree of impairment of voluntary movement and the level of passive muscle hypertonia in the antagonist. Although overactivity of the antagonist muscle may play some role in disturbance of movements made at low velocities without an opposing load, antagonist activity during movements made against a load (i.e., under more natural conditions) was at or below normal levels, even in those patients with the most marked passive muscle hypertonia. It is concluded that agonist muscle paresis, rather than antagonist muscle hypertonia, plays the dominant role in the disturbance of voluntary elbow movement following stroke.     

Visual feedback has differential effects on reaching movements in Parkinson's and Alzheimer's disease

We examine the role of visual feedback in the programming and execution of reaching movement in patients with Parkinson's disease without cognitive impairment and patients with Alzheimer's disease without extrapyramidal signs. Controls were normally aging subjects. All subjects moved a cursor to targets on a digitizing tablet without seeing their limb. Starting and target positions were always visible on a screen while, during movement, cursor position was either visible or blanked. They were instructed to make uncorrected movements, as fast and as accurate as possible without minimizing reaction time. In absence of visual feedback, movement accuracy in patients with AD was severely impaired. Hand paths of parkinsonian patients were as accurate as normal subjects' with similar temporal velocity profiles and movement speed. With cursor feedback, accuracy was the same in the three groups, although movement speed and transport phase in patients with Alzheimer's disease were significantly reduced compared to the other groups. Also, movements of parkinsonian patients showed shorter transport phase and lower mean velocity than controls'. The different characteristics of the motor performance suggests that in the two diseases visual information is used differently for both motor programming and execution: patients with Alzheimer's disease, while scarcely using feed forward commands, relied on continuous on-line external cues. The correlation of motor performance with cognitive impairment argues against the hypothesis of basal ganglia involvement in AD. The motor abnormalities we found may represent early subclinical manifestation of apraxic disturbance. Parkinsonian patients showed higher reliance on feedback commands only with cursor feedback: this could be explained by their difficulty in engaging effectively automatic routines when distractors are present.     

Adaptation motor learning of arm movements in patients with cerebellar disease.

OBJECTIVE--To design a test of motor learning using arm movements in normal subjects and patients with cerebellar disease. METHODS--Elbow angle was continuously displayed as a cursor (a dot) on a computer screen, and subjects made ballistic elbow flexion and extension movements to try to move the cursor between two targets on the screen. The relation between the arm movement and its visual feedback was changed, and the subjects reacted by adapting the amplitude of their movements in subsequent trials. RESULTS--The consecutive errors showed exponential learning curves during adaptation, which were quantified by their steepness. Ten patients with isolated cerebellar or olivopontocerebellar degeneration had less steep learning curves than normal subjects, indicating a failure of adaptation motor learning in cerebellar disease. The results show that this test may be useful for the analysis of motor learning.     

Scaling of the size of the first agonist EMG burst during rapid wrist movements in patients with Parkinson''s disease.

Rapid wrist flexion movements were studied in a group of 10 patients with Parkinson's disease both on and off their normal drug therapy, and were compared with the same movements made by a group of eight normal individuals. When normal subjects made movements through 60 degrees, the first agonist burst of EMG activity in the wrist flexor muscles was longer and larger than that seen in movements of 15 degrees. If a large opposing load of 2.2 Nm was added, this also increased the size and duration of the first agonist EMG burst. Although the movements made by the patients were slower than those of normals, the size and duration of the first agonist EMG burst changed with movement size and added load in the normal way. This shows that patients can produce large, long bursts of EMG activity, but that there is a failure to match these parameters appropriately to the size of movement required. The effect of levodopa therapy on the movements was not dramatic. Although patients produced faster wrist movements when on medication than when off, the change was relatively small compared with the change seen in their overall clinical rating. Changes in the velocity of movements at a single joint are not a good reflection of the overall clinical state of patients with Parkinson's disease.     

Visual feedback has differential effects on reaching movements in Parkinson’s and Alzheimer’s disease

We examine the role of visual feedback in the programming and execution of reaching movement in patients with Parkinson’s disease without cognitive impairment and patients with Alzheimer’s disease without extrapyramidal signs. Controls were normally aging subjects. All subjects moved a cursor to targets on a digitizing tablet without seeing their limb. Starting and target positions were always visible on a screen while, during movement, cursor position was either visible or blanked. They were instructed to make uncorrected movements, as fast and as accurate as possible without minimizing reaction time. In absence of visual feedback, movement accuracy in patients with AD was severely impaired. Hand paths of parkinsonian patients were as accurate as normal subjects’ with similar temporal velocity profiles and movement speed. With cursor feedback, accuracy was the same in the three groups, although movement speed and transport phase in patients with Alzheimer’s disease were significantly reduced compared to the other groups. Also, movements of parkinsonian patients showed shorter transport phase and lower mean velocity than controls’. The different characteristics of the motor performance suggests that in the two diseases visual information is used differently for both motor programming and execution: patients with Alzheimer’s disease, while scarcely using feed forward commands, relied on continuous on-line external cues. The correlation of motor performance with cognitive impairment argues against the hypothesis of basal ganglia involvement in AD. The motor abnormalities we found may represent early subclinical manifestation of apraxic disturbance. Parkinsonian patients showed higher reliance on feedback commands only with cursor feedback: this could be explained by their difficulty in engaging effectively automatic routines when distractors are present.     

Influence of visual and proprioceptive afferences on upper limb ataxia in patients with multiple sclerosis

Our objective was to investigate how cooling of the arm and vision influence pointing movements in healthy subjects and patients with cerebellar limb ataxia due to clinically proven multiple sclerosis. An infrared video motion analysis system was used to record the unrestricted, horizontal pointing movements toward a target under three different conditions involving a moving, stationary, or imaginary target; a visual, or acoustic trigger; and vision or memory guidance. All three tasks were performed before and after cooling the arm in ice water. Patients had more hypermetric and slower pointing movements than controls under all tested conditions. Patients also had significantly larger three-dimensional finger sway paths during the postural phase and larger movement angles of the wrist joint. Memory-guided movements were the most hypermetric recorded in both groups. Cooling of the limb had no effect on amplitude or peak velocity of the pointing movement in either group under all tested conditions, but significantly reduced the three-dimensional finger sway path during the postural phase in patients with limb ataxia. Cooling-induced reduction of the finger sway was largest in those patients with the largest finger sway before cooling. In conclusion, the cooling-induced reduction of the proprioceptive afferent inflow, most probably of group I spindle afferents, reduces postural tremor of patients with cerebellar dysfunction.     

Coordination of eye and head movements during smooth pursuit in patients with vestibular failure.

During pursuit of smoothly moving targets with combined eye and head movements in normal subjects, accurate gaze control depends on successful interaction of the vestibular and head movement signals with the ocular pursuit mechanisms. To investigate compensation for loss of the vestibulo-ocular reflex during head-free pursuit in labyrinthine-deficient patients, pursuit performance was assessed and compared under head-fixed and head-free conditions in five patients with isolated bilateral loss of vestibular function. Target motion consisted of predictable and unpredictable pseudo-random waveforms containing the sum of three or four sinusoids. Comparison of slow-phase gaze velocity gains under head-free and head-fixed conditions revealed no significant differences during pursuit of any of the three pseudo-random waveforms. The finding of significant compensatory eye movement during active head movements in darkness in labyrinthine-deficient patients, which were comparable in character and gain to the vestibular eye movement elicited in normal subjects, probably explains the similarity of the head-fixed and head-free responses. In two additional patients with cerebellar degeneration and vestibular failure, no compensatory eye movement response was observed, implying that the cerebellum is necessary for the generation of such responses in labyrinthine-deficient patients.     

Multi-joint reaching movements and eye-hand tracking in cerebellar incoordination: investigation of a patient with complete loss of Purkinje cells.

Performance on an eye-hand tracking task and a multi-joint reaching movement to a visual target was studied in a patient with stable cerebellar ataxia and in control subjects. The patient subsequently died and a full neuropathological examination was performed. The neuropathological findings were similar to those seen in patients with paraneoplastic cerebellar degeneration, but no tumor was found at autopsy eight years after onset of the patient's cerebellar syndrome. A severe cerebellar cortical degeneration with complete Purkinje cell loss was demonstrated, whereas cerebellar nuclei and brainstem structures showed no neuronal loss. Tracking performance by the patient was characterized by abnormally large numbers of high velocity movements and hand direction reversals, and by excessive lagging of the hand behind the target in time. In the multi-joint reaching movement, the patient showed a delay in movement onset at the elbow joint compared to movement onset at the shoulder joint. The velocity profile of the movement at the shoulder joint was abnormal. The duration of the acceleration phase was poorly correlated with both peak angular velocity and the duration of the deceleration phase. One of the most striking findings was the inability of the patient to consistently produce the same movement direction from trial to trial while reaching to the same target. Our data suggests that the cerebellar cortex is involved in multiple aspects of motor control including visuomotor integration mechanisms.     

Timing factors in the coordination of speech movements

Speech movement coordination involves substantial timing adjustments among multiple degrees of muscles and movement freedom. The present investigation examined the kinematic and muscle timing adjustments associated with the production of select speech movements. For oral closing movements, the timing of the upper lip, lower lip, and jaw peak velocities were found to be tightly coupled, apparently reflecting a coordinative strategy. In contrast, oral opening movements demonstrated reduced temporal coupling and inconsistent sequencing across subjects. Overall, it appears that the temporal organization of speech movements varies with the specific movement goals. In order to evaluate the coordinative patterns for oral closing in detail, the temporal adjustments of multiple perioral muscles associated with the systematic closing peak velocity relations were examined. The relative timing of muscle onsets and peak EMG amplitudes was found to be predictably related to the peak velocity timing variations, suggesting that the motor commands are temporally scaled to generate changes in speaking conditions. It was also found that the mechanical properties of the speech articulators influence movement coordination and can be exploited to maximize movement efficiency. The systematic change in muscle timing characteristics for all synergistic muscles apparently reduces the degrees of freedom to control, thereby facilitating the coordination process.     

Physiological analysis of simple rapid movements in patients with cerebellar deficits.

Patients with cerebellar deficits made elbow flexion movements as rapidly as possible for three different angular distances. Electromyographic activity of biceps and triceps and the kinematics of the movements were analysed. Results were compared with those of normal subjects making both rapid and slow movements. In the patients, the first agonist burst of the biceps was frequently prolonged regardless of the distance or speed of the movement. The most striking kinematic abnormality was prolonged acceleration time. The pattern of acceleration time exceeding deceleration time was common in patients but uncommon in normal subjects. The best kinematic correlate of the duration of the first agonist burst was acceleration time. Altered production of appropriate acceleration may therefore be an important abnormality in cerebellar dysfunction for attempted rapid voluntary movements.     

Extraocular muscle function in adult-onset Pompe disease tested by saccadic eye movements

Glycogen storage disease type II (Pompe disease) affects mainly proximal skeletal muscles. Despite older histological evidence of extraocular muscle involvement, ocular motor palsies or other eye movement abnormalities are not considered part of the clinical picture.We investigated the dynamics of saccadic eye movements of five patients suffering from late-onset Pompe disease and compared their performance to that of age matched healthy controls. Horizontal rightward and leftward saccades were recorded binocularly, while subjects looked at LED targets placed at ±5°, 10° and 15° eccentricities.No differences in saccade amplitudes, peak velocities or durations were observed between controls and patients. More specifically, for 5° saccades, patients had a mean peak velocity of 146°/s with duration of 76 ms. For 10° and 15° saccades these values were 258°/s, 86 ms and 324°/s, 101 ms respectively, thereby lying well within one standard deviation of the mean of normal data. Moreover, saccadic amplitude accuracy was also unimpaired.These results indicate that patients with late onset Pompe disease perform fast and accurate horizontal saccades without evidence of muscle paresis or other ocular motor abnormalities. Reported histological abnormalities of extraocular muscles do not appear to have a phenotypic impact.     

Kinematics of fast wrist movements in manic-depressive illness chronically treated with lithium carbonate

Abstract

Lithium salts have been shown to impair kinematics of fast voluntary movements during acute intoxication. The aim of the present study was to determine whether lithium carbonate affected the kinematics of fast movements in patients chronically treated and who did not exhibit signs of neurotoxicity. We analysed fast wrist flexion movements in 6 healthy subjects, in 5 patients presenting a manic-depressive illness without treatment, and in 8 patients receiving lithium carbonate for a manic-depressive disease. The mean duration of treatment was 3.9±4.1 years, the mean daily dose 837±341 mg and the mean serum level 0.95±0. 15 mEq/l. Although mean movement amplitudes were similar in the 3 groups, the variability of fast movements was increased in patients receiving lithium salts. The ratio of maximum to average velocities (VmNaveJ was significantly higher in patients treated, and their movements were temporally asymmetrical, with a ratio ofacceleration duration divided by deceleration duration being lower than in the 2 other groups. These kinematic abnormalities show that a chronic treatment with lithium salts is associated with an impairment of the cerebellar control of fast single-joint movements. [Neural Res 1998; 20: 320-326]     

Impaired temporal prediction and eye-hand coordination in patients with cerebellar lesions

This study investigated the effect of cerebellar lesions on temporal prediction and coordination in eye and hand movements. Nine patients with cerebellar lesions were compared to controls while they made saccades with and without simultaneous pointing movements towards a target that was either temporally predictable or non-predictable. The direction and amplitude of the target step was always predictable. Patients made much more early and late saccades than controls, but an equal amount of visually triggered saccades. This suggests that inappropriate saccades could be suppressed during the preparation of a goal-directed saccade. Hand movement frequency did not differ between both groups. Thus, cerebellar lesions can induce inappropriate saccades more easily than inappropriate hand movements. Controls, but not patients, generated visually triggered saccades of shorter latencies when the target was temporally predictable. Thus, the patients could not use information about target timing to synchronise visually triggered saccades with the target. They could, however, use this information to improve the suppression of inappropriate saccades. Regarding coordination, patients showed impairments in synchronising saccades with hand movements. Nevertheless, hand movements led to an enhancement of anticipatory saccades in patients as in controls. Moreover, hand movements and temporal predictability affected saccadic accuracy in both groups similarly. These results suggest that cerebellar lesions do not generally prevent access to temporal information on the rhythm of a target sequence or the timing of a planned hand movement. More specifically, the cerebellum seems to be crucial for synchronizing saccades with such learned or planned temporal events.     

The Functional Role of the Cerebellum in Visually Guided Tracking Movement

We propose a new method to provide a functional interpretation of motor commands (i.e., muscle activities) and their relationship to movement kinematics. We evaluated our method by analyzing the motor commands of normal controls and patients with cerebellar disorders for visually guided tracking movement of the wrist joint. Six control subjects and six patients with cerebellar disorders participated in this study. We asked the subjects to perform visually guided smooth tracking movement of the wrist joint with a manipulandum, and recorded the movements of the wrist joint and activities of the four wrist prime movers with surface electrodes. We found a symmetric relationship between the second-order linear equation of motion for the wrist joint and the linear sum of activities of the four wrist prime movers. The symmetric relationship determined a set of parameters to characterize the muscle activities and their similarity to the components of movement kinematics of the wrist joint. We found that muscle activities of the normal controls encoded both the velocity and the position of the moving target, resulting in precise tracking of the target. In contrast, muscle activities of the cerebellar patients were characterized by a severer impairment for velocity control and more dependence on position control, resulting in poor tracking of the smoothly moving target with many step-like awkward movements. Our results suggest that the cerebellum plays an important role in the generation of motor commands for smooth velocity and position control.     

Proprioceptive regulation of voluntary ankle movements, demonstrated using muscle vibration, is impaired by Parkinson''s disease

OBJECTIVE: To test the hypothesis that the proprioceptive regulation of voluntary movement is disturbed by Parkinson's disease, the effects of experimental stimulation of proprioceptors, using muscle vibration, on the trajectories of voluntary dorsiflexion movements of the ankle joint were compared between parkinsonian and control subjects. METHODS: Twenty one patients with Parkinson's disease, on routine medication (levodopa in all but one), and an equal number of age matched, neurologically intact controls, were trained initially to make reproducible ankle dorsiflexion movements (20 degrees amplitude with a velocity of 9.7 degrees /s) following a visual "go" cue while movement trajectories were recorded goniometrically. During 50% of the experimental trials, vibration (105 Hz; 0.7 mm peak to peak) was applied to the Achilles tendon during the ankle movement to stimulate antagonist muscle spindles; vibrated and non-vibrated trials were interspersed randomly. Subjects' performance was assessed by measuring end point position-that is, the ankle angle attained 2 seconds after the visual "go" cue, from averaged (20 trials) trajectories. RESULTS: Statistical analysis of the end point amplitudes of movement showed that, whereas the amplitudes of non-vibrated movements did not differ significantly between patients with Parkinson's disease and controls, antagonist muscle vibration produced a highly significant reduction in the amplitudes of ankle dorsiflexion movements in both the patient and control groups. However, the extent of vibration induced undershooting produced in the patients with Parkinson's disease was significantly less than that in the controls; the mean vibrated/non-vibrated ratios were 0.86 and 0.54 for, respectively, the patient and control groups. CONCLUSIONS: The present finding of a reduction of vibration induced ankle movement errors in parkinsonian patients resembles qualitatively previous observations of wrist movements, and suggests that Parkinson's disease may produce a general impairment of proprioceptive guidance.