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Front. Neurol. | doi: 10.3389/fneur.2018.00084

Involuntary Neuromuscular Coupling between the Thumb and Finger of Stroke Survivors during Dynamic Movement

 Christopher L. Jones1* and Derek G. Kamper2
  • 1HD LifeSciences, United States
  • 2North Carolina State University, United States

Finger-thumb coordination is crucial to manual dexterity but remains incompletely understood, particularly following neurological injury such as stroke. While being controlled independently, the index finger and thumb especially must work in concert to perform a variety of tasks requiring lateral or palmar pinch. The impact of stroke on this functionally critical sensorimotor control during dynamic tasks has been largely unexplored. In this study, we explored finger-thumb coupling during close-open pinching motions in stroke survivors with chronic hemiparesis. Two types of perturbations were applied randomly to the index with a novel cable-actuated finger exoskeleton: a sudden joint acceleration stretching muscle groups of the index finger and a sudden increase in impedance in selected index finger joint(s). Electromyographic signals for specific thumb and index finger muscles, thumb tip trajectory, and index finger joint angles were recorded during each trial. Joint angle perturbations invoked reflex responses in the FDS, FDI, and EDC muscles of the index finger and heteronymous reflex responses in FPB of the thumb (p<0.017). Phase of movement played a role as a faster peak reflex response was observed in FDI during opening than during closing (p<0.002) and direction of perturbations resulted in shorter reflex times for FDS and FDI (p<0.012) for extension perturbations. Surprisingly, when index finger joint impedance was suddenly increased, thumb-tip movement was substantially increased, maintaining aperture and increasing movement from 2 cm to 10 cm (p<0.001). A greater effect was seen during the opening phase (p<0.044). Thus, involuntary finger-thumb coupling was present during dynamic movement, with perturbation of the index finger impacting thumb activity. The degree of coupling modulated with the phase of motion. These findings reveal a potential mechanism for direct intervention to improve post-stroke hand mobility, and provides insight on prospective neurologically oriented therapies.

Keywords: exoskeleton, motor control, coupling, Reflex, Hand, robot, Rehabilitation

Received: 29 Jun 2017; Accepted: 06 Feb 2018.

Edited by:

Xiaogang Hu, University of North Carolina at Chapel Hill, United States

Reviewed by:

Sheng Li, University of Texas Health Science Center at Houston, United States
Jun Yao, Northwestern University, United States
Jongsang Son, Shirley Ryan AbilityLab, United States  

Copyright: © 2018 Jones and Kamper. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Christopher L. Jones, HD LifeSciences, Boston, United States, christopherljones@gmail.com