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BACKGROUND: Unilateral middle cerebral artery infarction has been reported to impair bilateral hand grasp. METHODS: Individuals (5 males and 5 females; age 33-86 years) with chronic unilateral middle cerebral artery stroke (4 right lesions and 6 left lesions) repeatedly lifted a 260-g object. Participants were then trained to lift the object using visuomotor feedback via an oscilloscope that displayed their actual grip force (GF) and a target GF, which roughly matched the physical properties of the object. RESULTS: The subjects failed to accurately modulate the predictive GF when relying on somatosensory information from the previous lifts. Instead, for all the lifts, they programmed excessive GF equivalent to the force used for the first lift. The predictive GF was lowered for lifts following the removal of the visual feedback. The mean difference in predictive GF between the lifts before and after visual training was significant (4.35 +/- 0.027 N; P <or= .001; 95% confidence interval CI = 3.80-4.88). After removal of visual feedback, there was also a significant mean difference in the applied predictive GF between the "early" and "late" lifts (0.78 +/- 0.029 N; P <or= .006; 95% CI = 0.22-1.35), demonstrating continued increase in predictive GF accuracy. CONCLUSION: Predictive or feedforward fingertip force generation is impaired in the ipsilesional hand when lifting a novel object with precision grip. Reacquisition of the motor forces for the grasp of objects is possible after stroke. Potentially, retraining grasp control for the ipsilesional hand may translate to improved function and motor learning within the contralesional hand.
Quaney et al. (Wed,) studied this question.