Dissociation of 'on-line' and 'off-line' visuomotor control of the arm by focal lesions in the cerebellum and brainstem

Visuomotor control of the arm was assessed in a single case study of a subj ect with focal lesions in the cerebellum and brainstem. A dissociation betw een 'on-line' and 'off-line' visuomotor control was revealed: impairments i n 'on-line' visuomotor control included inaccuracy of tracking velocity, in crease in spatial pointing variability and a delay in simple reaction time; whereas the patient was able to adapt to a gain change in 'off-line' visua l feedback during a pointing task, and his adaptation was less affected tha n that of control subjects by trial-to-trial random fluctuations in 'off-li ne' visual feedback. We conclude that focal damage in the cerebellar pedunc les may be principally responsible for this dissociation. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.