THE CANADIAN JOURNAL OF NEUROLOGICAL SCIENCES Cerebellar Dysfunction of Movement and Perception

This review describes some characteristics of patients with cerebellar lesions, including limb movements, changes in motor planning and disturbances in time-dependent perception. The delay in movement initiation can be explained by a delay in onset of movement-related discharge of neurons in motor cortex. Disorders of movement termination (hypermetria) are accompanied by asymmetric velocity profiles and by prolonged agonist and delayed antagonist EMG activity necessary to brake the movement. During complex movements in three-dimensional space, the cerebellum contributes to timing between single components of a movement, scales the size of muscular action, and coordinates the sequence of agonists and antagonists. The basic structure of motor programs is not generated exclusively within the cerebellum and patients with cerebellar lesions can use precuing information to improve their motor performance. Time-dependent perception in the auditory and visual domains are disturbed in patients with cerebellar lesions. RESUME: Dysfonction cerebelleuse du mouvement et de la perception. Cette revue decrit certaines caracteristiques de patients atteints de lesions cerebelleuses, particulierement en ce qui a trait aux mouvements des membres, aux changements dans la planification motrice et aux perturbations de la perception temporelle. Le delai dans 1 'initiation du mouvement peut etre explique par un delai dans le debut de la decharge, reliee au mouvement, des neurones moteurs corticaux. Les desordres de la fin du mouvement (hypermetrie) sont accompagnes par des profils de velocite asymetriques, ainsi qu'une prolongation de l'activite agoniste et un delai de l'activite antagoniste EMG necessaires pour freiner le mouvement. Pendant les mouvements complexes dans un espace tri-dimensionnel, le cervelet contribue a la synchronisation entre chacune des composantes d'un mouvement, ajuste l'amplitude de Faction musculaire et coordonne la sequence de Taction des agonistes et des antagonistes. La structure de base des programmes moteurs n'est generalement pas exclusivement localisee dans le cervelet et les patients qui ont des lesions cerebelleuses peuvent utiliser des elements de programmes deja connus comme indices pour ameliorer leur performance motrice. La perception temporelle dans les domaines auditifs et visuels est perturbee chez les patients ayant une lesion cerebelleuse. Can. J. Neurol. Sci. 1993; 20 (Suppl. 3): S62-S69 Disorders of the cerebellum result in clinical signs and symptoms that were comprehensively described and summarized by Holmes in 1917,' 1922 and 1939 and later by Dow and Moruzzi as well as Gilman et al. Lesions of the lateral parts of the posterior cerebellar hemisphere cause dyssynergia, dysmetria, dysdiadochokinesia, and dysarthria. Damage to the cerebellar vermis and the anterior lobe results in ataxia of stance and gait. Lesions of flocculus and paraflocculus result in an inability to stabilize a visual target on the retina. The cerebellum therefore, despite its homogeneous structure may be subdivided into functional compartments, and specific motor functions can be ascribed to these subunits." Despite considerable knowledge from animal and human physiology and pathophysiology," we still lack a widely-accepted hypothesis of the principal way in which the uniform anatomical structure of the intrinsic cerebellar network contributes to the control of movement. This review 1) will describe the features of pathological versus normal limb movements in cerebellar disorders, 2) will discuss the changes in motor planning in patients with cerebellar lesions and 3) will report disturbances in time-dependent perception with cerebellar dysfunction. PATHOPHYSIOLOGY OF CEREBELLAR DISORDERS