Elsevier

Neuroscience Letters

Volume 234, Issues 2–3, 3 October 1997, Pages 99-102
Neuroscience Letters

Load compensation tasks evoke tremor in cerebellar patients: the possible role of long latency stretch reflexes

https://doi.org/10.1016/S0304-3940(97)00681-2Get rights and content

Abstract

`Tremor' is one of the clinical signs of cerebellar dysfunction. Its nature remains subject to debate, one hypothesis being that of a predominant role of peripheral afferences in its genesis. This study was designed to study whether load compensating tasks, evoking sudden stretch, and thus stimulation of peripheral afferences induced tremor in cerebellar patients. We study the kinematics and EMG pattern of a load compensating task which consists of maintaining a constant elbow position despite the onset and cessation of a 2 Nm torque loading the elbow flexors in eight cerebellar patients and six controls. Angular position and velocity, and EMG of the biceps and triceps are recorded at a sampling rate of 1 kHz. In normal subjects, trajectories are simple with little overshoot of the aimed position. EMG analysis shows a long latency stretch response (LLSR) which initiates a phasic and then tonic voluntary activity. In cerebellar patients, the two prominent cinematic features are hypermetria and tremor. The stretch response is of the same latency, but the EMG pattern is modified with bursts of activity related to the tremor. These results show severe perturbations of load compensating tasks in cerebellar patients. We discuss the possible role of the exaggeration of LLSR in both hypermetria and tremor.

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    The PC1 for the control group, which had high communality with tremors of distal segments, was susceptible to load addition as manifested with a newly emerged spectral peak in the 5–8 Hz band (Fig. 6a). Although the source of the load-dependent 5–8 Hz tremor peak is still a matter of lively debate, several lines of indirect evidence indicate that the long-latency transcortical loops might play an important role (Elble and Randall, 1978; Gielen et al., 1988; Richard et al., 1997). Employing a closed-loop model, Arihara and Sakamoto (1999) successfully predicted the 5–8 Hz tremor peak following load superimposition, when a high ratio of gain in the supraspinal pathway to gain in spinal pathway was assumed (Arihara and Sakamoto, 1999).

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