ABSTRACT Lifting objects is based on the anticipatory programming of grip forces, where large objects are expected to be heavier than small ones, thus requiring higher grip forces. Also, it has been shown that when the size of the object does not match its anticipated weight, grip and load forces are adjusted based on haptic input to match the object’s true weight. The basal ganglia have been shown to have a role in the modulation of the magnitude and timing of grip force. Thus, it was of interest to investigate the role of the basal ganglia in: a) the control of grip and load force when lifting objects where the size and weight corresponded (control trials) and b) the adjustments of grip and load force to unexpected perturbations caused by a mismatch between an objects’ size and weight (perturbed trials). We tested an individual (RI) with a unilateral lesion to the basal ganglia as well as two healthy age-matched control subjects. For the control trials, RI’s contralesional hand showed lower peak grip force as well as lower grip force variability when compared to his ipsilesional hand and control subjects. RI showed no evidence of grip/load force adjustments in response to the perturbations, while the control subjects showed the expected adjustment patterns. These results suggest that impairments of the basal ganglia in RI led to overly stereotypical programming of grip and load forces in the contralesional hand that was highly dependent on visual size cues. While visual feedback could be used to modify the programming of an upcoming trial, there was no evidence that on-line feedback could be used by RI.
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