Load compensation tasks evoke tremor in cerebellar patients: the possible role of long latency stretch reflexes Isabelle Richard a, *, Michel Guglielmi b , Robert Boisliveau b , Brigitte Perrouin-Verbe a , Isabelle Mauduyt de la Gre `ve a , Bernard Bioulac c , Pierre Guiheneuc d , Jean-Franc ¸ois Mathe ´ a a Service de Re ´ e ´ ducation fonctionnelle, Ho ˆ pital St jacques 85, rue St jacques, 44093 Nantes cedex, France b Laboratoire d’Automatique de Nantes UA CNRS 823, Ecole Centrale Nantes, Nantes, France c Laboratoire de Neurophysiologie, UMR CNRS 5543, Universite ´ de Bordeaux II, Bordeaux, France d Laboratoire d’explorations fonctionnelles, C.H.U Nantes, Nantes, France Received 11 April 1997; received in revised form 29 August 1997; accepted 29 August 1997 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.  1997 Elsevier Science Ireland Ltd. Keywords: Load compensation; Long latency responses; Hypermetria; Tremor; Cerebellum; Human Since the first description [1,8] of cerebellar syndromes ‘tremor’ has been considered as one of the main signs of cerebellar dysfunction. However it is often difficult to dis- tinguish tremor from voluntary corrections of hypermetric movements and its exact nature remains subject to debate. There are two major theories [10]. The first is that of a central oscillator generating the tremor [13]. The only argu- ment for this hypothesis is the publication of data [12] showing that cerebellar tremor persists after dorsal rhizot- omy in monkeys. This result has not, to our knowledge been replicated since. The second hypothesis, which has received both electrophysiological [9] and clinical [3] support is that of the role of peripheral afferences in the generation of ‘tremor’. If peripheral, especially fusorial afferences play a major role, then load compensating tasks, which have been extensively studied in normal subjects and a variety of diseases, should provoke tremor in cerebellar patients. The aim of this study is to analyse the cinematics of load compensating tasks in cerebellar patients and determine whether sudden torque variations provoke tremor. Six controls and eight patients (Table 1) with pure cere- bellar syndromes were included. All patients had significant dysmetria at the finger-to-nose test and were hypotonic. They also exhibited marked ataxia. The subject sat, with one arm strapped in a splint composed of an upper arm and a forearm portion. The forearm portion could rotate around a vertical axis, allowing flexion and extension move- Neuroscience Letters 234 (1997) 99–102 0304-3940/97/$17.00  1997 Elsevier Science Ireland Ltd. All rights reserved PII S0304-3940(97)00681-2 * Corresponding author. Tel.: +33 2 40846177; fax: +33 2 40846176.