Syndrome-Specific Deficits of Performance and Effects of Practice on Arm Movements with Deafferentation due to Posterior Thalamic Lesion

Abstract

Aiming and tapping movements were analysed repeatedly over a three-week period in a patient who was hemideafferented due to an ischaemic posterior thalamic lesion. Contrasting behaviour observed in six healthy subjects, nine hemiparetic patients and one patient with hemianopic stroke, allowed the determination of behavioural deficits related to deafferentation. Finger tapping was not impaired specifically and did not improve with practice in the deafferented patient. When aiming movements were investigated, accuracy of the first, largely preprogrammed, phase of movement and timing of the late homing-in phase were impaired specifically in the deafferented patient. Practice led to a step-like change in preprogramming amplitude of the ballistic movement component, a gradual improvement of temporal efficiency of the early movement phase and a more marked improvement of the homing-in phase. Qualitatively comparable but quantitatively less marked effects of practice were documented for hemiparetic patients. These results demonstrated that deafferentation affects preprogrammed aspects of movement and those influenced by current control and that motor learning is possible with central deafferentation, even for aspects of performance that are impaired specifically. It is postulated that motor learning was mediated by changes in strategy (motor programming) and improved efficiency of intact motor control processes (visuomotor control).