[RECRUITMENT PATTERNS OF HOMOLOGOUS MUSCLES DURING UNILATERAL MOVEMENT IN HEMIPARETIC SUBJECTS].

INTRODUCTION: The presence of unintentional muscular activity, with or without overt movement, in the homologue muscle contralateral to the limb being activated voluntarily, has been documented in both healthy and hemi-paretic populations. This activity has been termed contra-lateral motor irradiation (CMI), mirror movement, associated movement, motor overflow or synkinesis.

AIMS: To characterize the CMI phenomenon amongst healthy controls and patients with varying degrees of motor ability and also to assess the ability to consciously control this phenomenon.

METHODS: A cross-sectional design was used to study sub-acute (within 6 weeks of the insult) stroke patients; assessments were performed within two weeks of commencing rehabilitation and again after 4 weeks. Healthy controls were assessed once. A simple motor task, unilateral extension of wrist and fingers, was examined. Concomitant muscular activity of the homologue muscle on the contralateral upper limb was the focus of interest; EMG activation was monitored on both sides. The Fugl-Meyer test was used to assess the residual motor capacity of the upper limb.

RESULTS: CMI was demonstrated only in the non-paretic hand during voluntary activation of the paretic hand. The study group, unlike the control group, was unable to consciously reduce CMI.

CONCLUSIONS: Although the mechanisms underlying CMI are poorly understood, they reflect an important aspect of inter-hemispheric relationship in motor control. In stroke patients, CMI monitoring by surface EMG can be used to assess its characteristics following damage to different elements of the motor system.