vendex and Cerebellar-Diseases

We reported previously that patients with cerebellar deficits were unable to scale the magnitude of their early automatic postural responses to the predicted amplitudes of surface translations based on central set from prior experience. The present study investigated whether this deficit in set-dependent amplitude scaling was based predominantly on the cerebellar patient's disability (i) to predict perturbation amplitudes on the basis of prior experience, (ii) to scale the gain or magnitude of upcoming postural responses or (iii) to habituate postural responses. The increase in size of the early postural response when a larger than actual platform amplitude was expected and decrease when a smaller one was expected was defined as a measure of set-dependent amplitude prediction. The suppression of the postural response when the same platform velocity was repeated was used as a measure of habituation. The correlation between the size of early postural responses and platform amplitudes when presented serially, but not randomly, tested the ability to scale the gain of postural responses based on prior experience. Results show that although cerebellar patients could predict perturbation amplitudes based on prior experience, they could not use this prediction to modify precisely the gain of responses. The ability to habituate the magnitude of postural responses was not affected by cerebellar lesions. Thus, the cerebellum might not be critical for predicting upcoming events or for habituating to repeated postural stimuli, although it is important for accurate tuning of response gain based on prediction.

Topics: Adult; Aged; Ankle; Cerebellar Diseases; Female; Habituation, Psychophysiologic; Humans; Leg; Male; Middle Aged; Motion Perception; Muscles; Posture; Psychomotor Performance; Random Allocation; Torque

Damage to the cerebellum causes characteristic movement abnormalities but is thought to have minimal impact on somatosensory perception. Traditional clinical assessments of patients with cerebellar lesions reveal no perceptual deficits despite the fact that the cerebellum receives substantial somatosensory information. Given that abnormalities have been reported in predicting the visual consequences of movement, we suspect that the cerebellum broadly participates in perception when motor output is required (i.e., active perception). Thus we hypothesize that cerebellar integrity is essential for somatosensory perception that requires motor activity, but not passive somatosensory perception. We compared the perceptual acuity of human cerebellar patients to that of healthy control subjects in several different somatosensory perception tasks with minimal visual information. We found that patients were worse at active force and stiffness discrimination but similar to control subjects with regard to passive cutaneous force detection, passive proprioceptive detection, and passive proprioceptive discrimination. Furthermore, the severity of movement symptoms as assessed by a clinical exam was positively correlated with impairment of active force perception. Notably, within the context of these perceptual tasks, control subjects and cerebellar patients displayed similar movement characteristics, and hence differing movement strategies are unlikely to underlie the differences in perception. Our results are consistent with the hypothesis that the cerebellum is vital to sensory prediction of self-generated movement and suggest a general role for the cerebellum in multiple forms of active perception.

Topics: Adult; Aged; Cerebellar Diseases; Cerebellum; Discrimination, Psychological; Electromyography; Female; Humans; Male; Middle Aged; Muscle, Skeletal; Perception; Proprioception; Torque

Numerous studies have shown torque control to be an important factor in grip-force control. This study introduces a novel task which allows quantification of the dynamics of torque development while increasing grip forces during a task comparable to picking a raspberry. The performance of this task was analysed in two healthy subjects and two cerebellar patients. Individual grip forces and finger positions on a grip rod were analysed using a recently developed technique [Kutz DF, Woelfel A, Timmann D, Kolb FP. Detection of changes in grip forces on a sliding object. J Neurosci Methods 2007;166:250-8]. Levers and torques were derived from grip forces and geometric properties of the grip rod. The analysis of this task performance provides evidence that healthy subjects are able to minimise torque despite increasing grip force, whereas the cerebellar patients tested increased torque disproportionately with increasing grip forces, whereby these high torques were due primarily to the patients' inability to optimise individual finger positions on the rod. Patients tried to compensate their ataxia-based insecurity by employing higher grip forces, resulting in disproportionately higher torques and increased instability, whereupon they again increased grip force, thus establishing a vicious circle. The analysis of this task suggests that effective rehabilitation strategies must be aimed at interrupting this circle.

Topics: Adult; Cerebellar Diseases; Female; Fruit; Hand Strength; Humans; Male; Middle Aged; Nonlinear Dynamics; Psychomotor Performance; Reaction Time; Task Performance and Analysis; Torque; 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