The effect of stroke on motor selectivity for force control in single- and multi-finger force production tasks

Abstract

BACKGROUND: The stroke patients have difficulties in both voluntary muscle contraction and individual movements. However, there is a lack of quantitative analysis focusing on decreased finger control in stroke patients. OBJECTIVES: The purpose of the study was to identify the changes in motor selectivity in stroke patients during a finger force production task. METHODS: Fifteen stroke patients and fifteen control subjects were asked to perform maximum voluntary force (MVF) production during single-and multi-finger force tasks. Finger interaction indices such as force independence (FI) and force sharing deviation (FSD) were analyzed using measured individual finger forces. RESULTS: MVF analysis in the impaired hand of stroke patients showed that they produced 31% or 41% lower force than their unimpaired hand or the control hand, respectively. For the finger interaction indices, the stroke patients' impaired hand had lower FI and higher FSD than their unimpaired hand or the normal subjects' hand. CONCLUSION: The lower FI and higher FSD show that stroke patients have a limited ability to produce force independently and to synchronize produced multi-finger force, respectively. These results have a negative impact on the selectivity of their motor control. In terms of rehabilitation, we expect that the finger interaction indices used in the present study can quantify motor selectivity in the damaged central nervous system.