vendex and Cerebellar-Ataxia

Prior work has shown that cerebellar subjects have difficulty adjusting for interaction torques that occur during multi-jointed movements. The purpose of this study was to determine whether this deficit is due to a general inability to generate sufficient levels of phasic torque inability or due to an inability to generate muscle torques that predict and compensate for interaction torques. A second purpose was to determine whether reducing the number of moving joints by external mechanical fixation could improve cerebellar subjects' targeted limb movements. We studied control and cerebellar subjects making elbow flexion movements to touch a target under two conditions: 1) a shoulder free condition, which required only elbow flexion, although the shoulder joint was unconstrained and 2) a shoulder fixed condition, where the shoulder joint was mechanically stabilized so it could not move. We measured joint positions of the arm in the sagittal plane and electromyograms (EMGs) of shoulder and elbow muscles. Elbow and shoulder torques were estimated using inverse dynamics equations. In the shoulder free condition, cerebellar subjects made greater endpoint errors (primarily overshoots) than did controls. Cerebellar subjects' overshoot errors were largely due to unwanted flexion at the shoulder. The excessive shoulder flexion resulted from a torque mismatch, where larger shoulder muscle torques were produced at higher rates than would be appropriate for a given elbow movement. In the shoulder fixed condition, endpoint errors of cerebellar subjects and controls were comparable. The improved accuracy of cerebellar subjects was accompanied by reduced shoulder flexor muscle activity. Most of the correct cerebellar trials in the shoulder fixed condition were movements made using only muscles that flex the elbow. Our findings suggest that cerebellar subjects' poor shoulder control is due to an inability to generate muscle torques that predict and compensate for interaction torques, and not due to a general inability to generate sufficient levels of phasic torque. In addition, reducing the number of muscles to be controlled improved cerebellar ataxia.

Topics: Adult; Aged; Biomechanical Phenomena; Cerebellar Ataxia; Elbow Joint; Electromyography; Humans; Joints; Middle Aged; Movement; Muscle, Skeletal; Shoulder Joint; Torque

Impedance control enables humans to effectively interact with their environment during postural and movement tasks, adjusting the mechanical behavior of their limbs to account for instability. Previous work has shown that people are able to selectively modulate the end-point stiffness of their arms, adjusting for varying directions of environmental disturbances. Behavioral studies also suggest that separate controllers are used for impedance modulation versus joint torque coordination. Here we tested whether people with cerebellar damage have deficits in impedance control. It is known that these individuals have poor motor coordination, which has typically been attributed to deficits in joint torque control. Subjects performed a static postural maintenance task with two different types of directional force perturbations. On average, patients with cerebellar ataxia modified stiffness differentially for the two perturbation conditions, although significantly less than age-matched control subjects. Thus cerebellar damage may impair the ability to modulate arm impedance. Surprisingly, the patients' intact ability to generally alter their limb stiffness during the postural task (albeit less than age-matched control subjects) improved their movement performance in a subsequent tracing task. The transfer of stiffness control from the static to the movement task may be a strategy that can be used by patients to compensate for their motor deficits.

Topics: Aged; Arm; Biomechanical Phenomena; Case-Control Studies; Cerebellar Ataxia; Female; Humans; Joints; Male; Middle Aged; Movement; Postural Balance; Range of Motion, Articular; Torque

Quantitative evaluation of cerebellar ataxia is crucial for precise evaluation of cerebellar diseases. In particular, it is essential to capture anomaly of the causal motor commands as well as the resultant movement for the ataxia. In this paper, we propose a new method to make a quantitative evaluation of the cerebellar ataxia based on EMG signals. As an experimental task, we asked subjects to perform step-tracking wrist movements with a manipulandum, and recorded wrist joint movements and muscle activities of four wrist prime movers with surface electrodes. The subjects included fourteen patients with cerebellar diseases and thirteen normal controls. We succeeded to extract two parameters from the EMG signals of the four wrist prime movers, which characterize the pathological patterns of muscle activities for the cerebellar ataxia, Total Co-contraction Level (TCL) and Directionality of Muscle Activity (DMA). We found that the two parameters were useful to characterize pathological patterns of muscle activities in cerebellar ataxia. Consequently, it is expected that our proposed method is useful not only in tracking condition of cerebellar patients but also in evaluating the effects of a treatment or neuro-rehabilitation aiming at the normalization of motor commands.

Topics: Biomechanical Phenomena; Case-Control Studies; Cerebellar Ataxia; Electromyography; Humans; Movement; Muscle Contraction; Muscle Tonus; Muscles; Torque; Wrist Joint

Because damage to the cerebellum results in characteristic movement incoordination known as "ataxia," it has been hypothesized that it is involved in estimation of limb dynamics that occur during movement. However, cerebellar function may extend beyond movement to force control in general, with or without movement. Here we tested whether the cerebellum is involved in controlling force separate from estimating limb dynamics and whether ataxia could result from a deficit in force control. We studied patients with cerebellar ataxia controlling their arm force isometrically; in this condition arm dynamics are absent and there is no need for (or effect from an impairment in) estimations of limb dynamics. Subjects were required to control their force magnitude, direction, or both. Cerebellar patients were able to match force magnitude or direction similarly to control subjects. Furthermore, when controlling force magnitude, they intuitively chose directions (not specified) that required minimal effort at the joint level--this ability was also similar to control subjects. In contrast, cerebellar patients performed significantly worse than control subjects when asked to match both force magnitude and direction. This was surprising, since they did not exhibit significant impairment in doing either in isolation. These results show that cerebellum-dependent computations are not limited to estimations of body dynamics needed for active movement. Deficits occur even in isometric conditions, but apparently only when multiple degrees of freedom must be controlled simultaneously. Thus a fundamental cerebellar operation may be combining/coordinating degrees of freedom across many kinds of movements and behaviors.

Topics: Adult; Aged; Arm; Case-Control Studies; Cerebellar Ataxia; Cerebellum; Female; Humans; Isometric Contraction; Joints; Male; Middle Aged; Torque

Damage to the cerebellum can cause significant problems in the coordination of voluntary arm movements. One prominent idea is that incoordination stems from an inability to predictively account for the complex mechanical interactions between the arm's several joints. Motivated by growing evidence that corrective feedback control shares important capabilities and neural substrates with feedforward control, we asked whether cerebellar damage impacts feedback stabilization of the multijoint arm appropriate for the arm's intersegmental dynamics. Specifically, we tested whether cerebellar dysfunction impacts the ability of posterior deltoid to incorporate elbow motion in its long-latency response (R2 = 45-75 ms and R3 = 75-100 ms after perturbation) to an unexpected torque perturbation. Healthy and cerebellar-damaged subjects were exposed to a selected pattern of shoulder-elbow displacements to probe the response pattern from this shoulder extensor muscle. The healthy elderly subjects expressed a long-latency response linked to both shoulder and elbow motion, including an increase/decrease in shoulder extensor activity with elbow flexion/extension. Critically, cerebellar-damaged subjects displayed the normal pattern of activity in the R3 period indicating an intact ability to rapidly integrate multijoint motion appropriate to the arm's intersegmental dynamics. However, cerebellar-damaged subjects had a lower magnitude of activity that was specific to the long-latency period (both R2 and R3) and a slightly delayed onset of multijoint sensitivity. Taken together, our results suggest that the basic motor pattern of the long-latency response is housed outside the cerebellum and is scaled by processes within the cerebellum.

Topics: Adult; Aged; Case-Control Studies; Cerebellar Ataxia; Cerebellum; Feedback, Physiological; Humans; Joints; Middle Aged; Motion; Movement; Muscle, Skeletal; Reaction Time; Torque; Upper Extremity

The pathophysiological assessment of joint properties and voluntary motion in neurological patients remains a challenge. This is typically the case in cerebellar patients, who exhibit dysmetric movements due to the dysfunction of cerebellar circuitry. Several tools have been developed, but so far most of these tools have remained confined to laboratories, with a lack of standardization. We report on a new device which combines the use of electromyographic (EMG) sensors with haptic technology for the dynamic investigation of wrist properties. The instrument is composed of a drivetrain, a haptic controller and a signal acquisition unit. Angular accuracy is 0.00611 rad, nominal torque is 6 N·m, maximal rotation velocity is 34.907 rad/sec, with a range of motion of -1.0472 to +1.0472 rad. The inertia of the motor and handgrip is 0.004 kg·m2. This is the first standardized myohaptic instrument allowing the dynamic characterization of wrist properties, including under the condition of artificial damping. We show that cerebellar patients are unable to adapt EMG activities when faced with an increase in damping while performing fast reversal movements. The instrument allows the extraction of an electrophysiological signature of a cerebellar deficit.

Topics: Adult; Aged; Case-Control Studies; Cerebellar Ataxia; Computer Simulation; Electromyography; Female; Humans; Male; Middle Aged; Motion; Muscle Contraction; Muscle, Skeletal; Range of Motion, Articular; Rotation; Torque; Wrist; Wrist Joint; Young Adult

It has been suggested that the cerebellum is an important contributor to CNS prediction and control of intersegmental dynamics during voluntary multijoint reaching movements. Leg movements subserve different behavioral goals, e.g., locomotion versus voluntary stepping, which may or may not be under similar dynamic control. The objective was to determine whether cerebellar leg hypermetria (excessive foot elevation) during obstacle avoidance in locomotion and voluntary stepping could be attributed to a particular deficit in appropriately controlling intersegmental dynamics. We compared the performance of eight individuals with cerebellar damage to eight healthy controls as they walked or voluntarily stepped in place over a small obstacle. Joint kinematics and dynamics were calculated during swing phase for both movement contexts. The kinematic analysis showed that hypermetria occurred during both walking and stepping and was associated with excessive knee flexion. When present, the amplitude of hypermetria was greater during stepping compared to walking. During stepping, subjects with cerebellar damage produced excessive knee flexor muscle torques and consequently overcompensated for interaction and gravitational torques normally used to decelerate the limb. During walking, the torque pattern was very similar to that of control subjects walking over a taller obstacle, and therefore might be a voluntary compensatory strategy to avoid tripping. Our results show that the extent of kinematic and dynamic abnormalities associated with cerebellar leg hypermetria is context-specific, with more fundamental abnormalities of leg dynamics being apparent during stepping as opposed to walking.

Topics: Adult; Aged; Analysis of Variance; Avoidance Learning; Biomechanical Phenomena; Cerebellar Ataxia; Cerebellar Diseases; Female; Humans; Leg; Locomotion; Male; Middle Aged; Movement; Torque; Walking

A simple paradigm was used to investigate how patients with cerebellar lesions cope with the need to correct for joint interactions during a multi-joint movement. Normal subjects and patients with cerebellar degeneration performed fast unconstrained elbow flexions with the instruction to voluntarily fixate the shoulder joint. Angular kinematics and inverse dynamics analyses were performed. A susceptibility index quantified how strong-concomitant shoulder-motion depended on interactions from the elbow. Amplitudes of involuntary shoulder movements increased with elbow movement speed and were generally larger in patients. Susceptibility indices were smaller in patients, indicating a more variable compensatory response, however, increased with elbow movement speed. We conclude that patients were significantly less able to 'tune' their postural stabilizing response to match interaction torques. However, the velocity dependence of this effect points to a deficit in generating normal levels of phasic torque.

Topics: Adult; Biomechanical Phenomena; Cerebellar Ataxia; Elbow Joint; Humans; Middle Aged; Motor Neurons; Movement; Muscle, Skeletal; Shoulder Joint; Torque

1. We studied seven subjects with cerebellar lesions and seven control subjects as they made reaching movements in the sagittal plane to a target directly in front of them. Reaches were made under three different conditions: 1) "slow-accurate," 2) "fast-accurate," and 3) "fast as possible." All subjects were videotaped moving in a sagittal plane with markers on the index finger, wrist, elbow, and shoulder. Marker positions were digitized and then used to calculate joint angles. For each of the shoulder, elbow and wrist joints, inverse dynamics equations based on a three-segment limb model were used to estimate the net torque (sum of components) and each of the component torques. The component torques consisted of the torque due to gravity, the dynamic interaction torques induced passively by the movement of the adjacent joint, and the torque produced by the muscles and passive tissue elements (sometimes called "residual" torque). 2. A kinematic analysis of the movement trajectory and the change in joint angles showed that the reaches of subjects with cerebellar lesions were abnormal compared with reaches of control subjects. In both the slow-accurate and fast-accurate conditions the cerebellar subjects made abnormally curved wrist paths; the curvature was greater in the slow-accurate condition. During the slow-accurate condition, cerebellar subjects showed target undershoot and tended to move one joint at a time (decomposition). During the fast-accurate reaches, the cerebellar subjects showed target overshoot. Additionally, in the fast-accurate condition, cerebellar subjects moved the joints at abnormal rates relative to one another, but the movements were less decomposed. Only three subjects were tested in the fast as possible condition; this condition was analyzed only to determine maximal reaching speeds of subjects with cerebellar lesions. Cerebellar subjects moved more slowly than controls in all three conditions. 3. A kinetic analysis of torques generated at each joint during the slow-accurate reaches and the fast-accurate reaches revealed that subjects with cerebellar lesions produced very different torque profiles compared with control subjects. In the slow-accurate condition, the cerebellar subjects produced abnormal elbow muscle torques that prevented the normal elbow extension early in the reach. In the fast-accurate condition, the cerebellar subjects produced inappropriate levels of shoulder muscle torque and also produced elbow muscle torques

Topics: Adult; Case-Control Studies; Cerebellar Ataxia; Female; Humans; Joints; Kinesthesis; Male; Middle Aged; Movement; Reaction Time; Reproducibility of Results; Torque; Videotape Recording