Visual and mechanical control of postural and kinetic tremor in cerebellar system disorders

The influence of alterations in visual guidance and somaesthetic sensory inputs was studied in five patients with kinetic and postural tremor characteristic of cerebellar impairment. The patients performed wrist flexion-extension movements or movements about the shoulder with or without visual guidance. Different types of mechanical loads were applied to oppose the wrist movements. The tremor was greatest when the patients used visual cues to guide movements. Kinetic tremor was substantially suppressed during performance of similar movements that were not guided directly by vision. Viscous loads suppressed the tremor nearly linearly, whereas constant loads opposing extension enhanced the tremor. The postural tremor was not observed during isometric contractions. These results support the view that processing of visual information contributes to the impairment of movement in disorders with cerebellar-type tremor and that certain somaesthetic inputs can selectively influence the generation of postural tremor.