Upper Limb Position Matching After Stroke: Evidence for Bilateral Asymmetry in Precision but Not in Accuracy

Assessment and rehabilitation of the upper limb after stroke have focused primarily on the contralesional arm. However, increasing evidence highlights functional sensorimotor alterations also in the ipsilesional arm. This study aims to evaluate the position sense of both arms after stroke using a passive position matching task. We hypothesized that the ipsilesional arm would have higher accuracy and precision than the contralesional arm but lower than the dominant arm in unimpaired participants. Additionally, we hypothesized a correlation in performance between the two arms in stroke survivors. The study included 40 stroke survivors who performed the proprioceptive test with both arms and 24 unimpaired participants who performed it with their dominant arm. During each trial, a planar robot moved their hand to a target and back. In the Participants had to indicate when their hand reached the target position in the second phase. We evaluated performance by computing the matching accuracy and precision. We found that the ipsilesional arm had similar matching accuracy but higher precision than the contralesional arm. Furthermore, only the matching accuracy of the two arms was correlated in the left and central regions of the workspace. When comparing stroke survivors to unimpaired participants, the ipsilesional arm exhibited significantly lower accuracy, yet not different precision. These findings support the notion that the ipsilesional arm is not 'unaffected' by stroke but rather 'less-affected', suggesting that stroke does not impact ipsilesional position sense precision. Additionally, the results suggest a dissociation between accuracy and precision in passive multi-joint position matching tasks.