Predictive control of muscle responses to arm perturbations in cerebellar patients

Abstract

Objectives-To examine changes in predictive control of early antagonist responses to limb perturbations in patients with defined lesions of the cerebellum. Methods-Eight cerebellar patients and eight sex and age matched control subjects participated. Subjects held a handle that was rotated around the elbow joint. They were instructed to hold the forearm at 90°fl exion against a mechanical perturbation. Extensor torque (5 Nm) was applied for 140 ms (pulse), or for 1400 ms (step) through an external motor. Motor responses were tested under two diVerent conditions of anticipatory information. In the expected condition, subjects anticipated and received a pulse. Under the unexpected condition, subjects expected steps, but received unexpected pulses. Biceps and triceps EMG as well as angular kinematics were compared between expected and unexpected pulse perturbations to quantify possible eVects of prediction. Results-In all healthy subjects, the degree of overshoot in the return flexion movement was significantly less in expected pulse perturbations compared with unexpected trials. The degree of amplitude reduction was significantly smaller in the patient group than in the control group (22.8% v 40.0%). During the expected trials, latency of peak triceps activity was on average 20% shorter in the control group, but 4% larger in the cerebellar patients. Conclusions-In the expected condition, controls achieved a significant reduction in angular amplitude by generating triceps activity earlier, whereas the ability to use prediction for adjusting early antagonist responses after limb perturbation was impaired in cerebellar patients. (J Neurol Neurosurg Psychiatry 2000;69:345-352)

BOLD Coherence Reveals Segregated Functional Neural Interactions When Adapting to Distinct Torque Perturbations

“…Executing adaptive control in the positional perturbation condition led to a stronger coherence between cortical-cerebellar sensorimotor regions than cortico-basal ganglia regions. This finding is consistent with and supports an extensive literature-based linking of the cerebellum in the prediction of sensorimotor events (Blakemore and Sirigu 2003; Dreher and Grafman 2002;Miall et al 1993;Nitschke et al 2003;Nixon 2003;Timmann et al 2000). In our study, this increased cerebellar-cortical coherence may likely be attributable to the increased effort in predicting the edges of the perturbation step.…”

Muscle Reflexes and Synergies Triggered by an Unexpected Support Surface Height During Walking

“…Animal and human studies have shown that cerebellar integrity is needed to respond in time and accurately to unexpected perturbations of arm movements (Shimansky et al 2004;Timmann et al 2000). However, the fast latencies that were observed in this study (47-69 ms) are too short for transcerebellar loops.…”

Cerebellar ataxia impairs modulation of arm stiffness during postural maintenance

“…Thus, while the ability to generally increase stiffness appears intact despite cerebellar degeneration, the cerebellum may be involved in controlling muscle cocontraction to directionally tune limb stiffness to instabilities. Similar to other studies reporting abnormal perturbation responses due to cerebellar deficits (Hermsdorfer et al 1994;Timmann et al 2000), we found no correlation between ataxia severity (ICARS score) and the ability to modulate the hand stiffness ellipse.…”