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Full text release has been delayed at the author's request until January 19, 2026

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Incorporating Stiffness Modulation into Intracortically-Controlled Upper Limb Neuromuscular Stimulation Systems

Johnson, Tyler
http://orcid.org/0000-0001-9225-3491
http://rave.ohiolink.edu/etdc/view?acc_num=case1701335192541056

Abstract Details

2023, Doctor of Philosophy, Case Western Reserve University, Biomedical Engineering.
Functional electrical stimulation (FES) of arm and hand muscles combined with decoded motor intentions from intracortical recordings can restore reaching ability to individuals with spinal cord injury. This research aims to improve FES generated arm movements by incorporating real-time modulation of limb stiffness in addition to limb kinematics. During normal arm movements people actively adjust the amount of cocontraction, or the degree to which opposing muscles are simultaneously active. Increasing cocontraction stiffens our limbs making them more resistant to external perturbations while decreasing cocontraction minimizes energy use and facilitates rapid movement. Optimizing the degree of cocontraction is particularly important for FES because excess cocontraction can lead to muscle fatigue and faster battery drain. Conversely, too little cocontraction can lead to poorly controlled movements that are prone to perturbations from the environment. First, we incorporated automated stiffness modulation into FES systems using a virtual arm model. After running many simulations, we found the optimal control method to automatically modulate limb stiffness based on the intended limb velocity command. Next, we built upon that method by addressing two key practical issues: 1) balancing stimulation across multiple redundant muscles, and 2) optimizing stimulation of biarticular muscles. With these advances, we demonstrate how to generate an upper limb FES control algorithm that is clinically practical to implement and allows one to control limb stiffness in addition to kinematics. Finally, with the goal of finding a neurally encoded volitional stiffness signal, we trained macaques with intracortical microelectrodes to perform an EMG controlled cursor task in which independent activation of antagonist muscles controlled one dimension and a separate dimension of movement was controlled by the cocontraction of the same muscles. Results revealed some neural signals correlated particularly with cocontraction rather than individual muscle activations. These neural signals were then used to modulate a stiffness dimension proving the validity of volitional stiffness decoding. Results from these studies will help improve restoration of reaching after paralysis by demonstrating a clinically practical stimulation control method that can incorporate both automated and volitional stiffness modulation.
Dawn Taylor (Advisor)
Roger Quinn (Committee Member)
A. Bolu Ajiboye (Committee Member)
Robert Kirsch (Committee Chair)
161 p.
Biomedical Engineering; Neurosciences
Neural Decoding; Functional Electrical Stimulation; Limb Stiffness; Brain Machine Interfaces; Brain Computer Interfaces

Recommended Citations

Citations

  • Johnson, T. (2023). Incorporating Stiffness Modulation into Intracortically-Controlled Upper Limb Neuromuscular Stimulation Systems [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1701335192541056

    APA Style (7th edition)

  • Johnson, Tyler. Incorporating Stiffness Modulation into Intracortically-Controlled Upper Limb Neuromuscular Stimulation Systems. 2023. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1701335192541056.

    MLA Style (8th edition)

  • Johnson, Tyler. "Incorporating Stiffness Modulation into Intracortically-Controlled Upper Limb Neuromuscular Stimulation Systems." Doctoral dissertation, Case Western Reserve University, 2023. http://rave.ohiolink.edu/etdc/view?acc_num=case1701335192541056

    Chicago Manual of Style (17th edition)

case1701335192541056
© 2023, all rights reserved.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.
Release 3.2.12