A defective control of small-amplitude movements in ... - Research

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BEHAVIOURAL BRAIN RESEARCH

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BehaviouralBrain Research 72 (1996) 57-62

Research report

A defective control of small-amplitude movements in monkeys with globus pallidus lesions: an experimental study on one component of pallidal bradykinesia M e r y e m A l a m y ", J e a n - C l a u d e P o n s a, D a n i e l l e G a m b a r e l l i b, E l i s a b e t h T r o u c h e a , a CNRS, UPR 9013, 31 chemin Joseph Aiguier, 13402 Marseille Cedex 20, France b Laboratoire d'Anatomh, Pathologique et de Neuropathologie, FacultO de Mddecine, 27 boulevard Jean Moulin, 13385 Marseille, France

Received 25 May 1994; revised 28 February 1995; accepted 28 February 1995

Abstract

The effects of globus pallidus (GP) lesion were examined in two monkeys trained to perform a visually guided pointing movement in simple and choice reaction time tasks involving small and large amplitude movements. The reaction time (RT) and the movement time (MT) were measured. The Y-axis error (EY) was also analyzed in order to assess the movement accuracy. Unilateral GP lesion was made by locally injecting an excitatory amino acid, quisqualic acid. GP lesion led to little change in the RTs (simple and choice RTs) and in the EY, whereas a large increase in the MT occurred. The MT impairments seem to have been correlated with the movement amplitude, since they were larger in the case of small-amplitude than large-amplitude movements. These results suggest that the GP may be involved in the control of small-amplitude rather than large-amplitude movements. As various studies have shown that proprioceptive cues are more strongly involved in the control of discrete than large-amplitude movement,;, the MT deficit, i.e., the bradykinesia observed here, may reflect a defective integration of proprioceptive information occurring afte:r GP lesion. Keywords: Globus pallidus; Reaction time task; Accuracyconstraint; Movementamplitude; Movementtime; Quisqualic acid lesion; Monkey

1. Introduction

The movement deficits resulting from impairment of the basal ganglia can be, either hyperkinetic in the case of involontary movements or hypokinetic, as in the case of the lengthening of movement initiation (akinesia) and decrease in the amplitude and velocity of volontary movements (bradykinesia). These findings are consistent with the idea that the basal ganglia may be involved in the control of both movement initiation and execution. Studies involving experiraental lesion of the basal ganglia outputs at the level of the globus pallidus (GP) have shown the existence of an impaired movement latency which seemed to depend on the task [2] and on the availability of visual cues [1,2]. An increase in the movement time was ahvays observed after G P lesion [5,14,19] The decrease observed in the amplitude of the * Correspondingauthor. Fax: (33) 91 77 50 83. 0166-4328/96/$9.50 © ElsevierScienceB.V. All rights reserved SSSDI 0166-4328 (96) 00048-8

initial agonist E M G burst occurring after pallidal lesion [12] may be partly responsible for the lengthening of the motor execution time recorded. The bradykinesia resulting from lesion of the substantia nigra (SN) [4,9,28,31,33], the other basal ganglia output structure, as well as that observed in patients with Parkinson's disease involved an increase in the movement time and in the movement variability [29]. Both in Parkinson's disease [ 10] as well as in animals with experimental SN lesions [3], the akinesia was correlated with the movement amplitude and was more marked in movements with large amplitudes. This suggests that the subjects had difficulty in controlling the movement amplitude after lesion of the basal ganglia. The aim of our study was to analyze the akinesia and bradykinesia resulting from pallidal lesions, particularly as regards the control of the movement amplitude. We therefore investigated the effects of G P lesion on monkeys' movement performances in two reaction time tasks involving large and small-amplitude movements.

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Meryem Alamy et aL/Behavioural Brain Research 72 (1996) 57-62

2. Materials and methods

2.1. Behavioral task Two Papio papio monkeys were used in these experiments. The subjects were trained to perform pointing tasks, the one consisting of a simple reaction time task (only subject R was tested in this paradigm) and the other consisting of a choice reaction time task involving a choice of amplitude. The subjects were placed in a working cage facing a vertical pointing board fitted with a handle on the lower part, on which they had to place their hand. After a variable preparatory period (500, 1000, 1500 or 2000 ms), they had to release the handle at the onset of a luminous signal, and point at the signal as accurately as possible with the index finger. The experimental paradigm used here has been described previously [30]. In the simple reaction time task (SRT), only the time of the target onset was unpredictable. In the choice reaction time task (CRT), the location of the target was also unpredictable (Fig. 1), and induced two kinds of movement in the same direction: movements with a large amplitude (target 29 cm from the handle) and those with a smaller amplitude (target 14 cm from the handle). The variables recorded (Fig. 1) were the reaction time (RT), defined as the time elapsing between the onset of the luminous signal and the handle release, the movement time (MT), taken to be the time elapsing between the handle release and the first contact of the finger and the pointing board, and the Y-axis error (EY). The EY were used to assess the movement accuracy, which was taken to be the mean distance between

Handle

the Y-axis coordinate of the target and the contact point, in millimeters. The monkeys received a juice reward whenever the movements were performed correctly, i.e., when 100