Motor Point Stimulation and its Role in Investigating and Modulating Neural Circuits

Yamashita, Taro 1, 2 ; Bergquist, Austin 1, 2 ; Yoshida, Takashi 1, 2 ; Masani, Kei 1, 2

1. Institute of Biomaterials and Biomedical Engineering, University of Toronto, 164 College Street, Toronto, Ontario M5S 3G9, Canada; Rehabilitation Engineering Laboratory, Lyndhurst Centre, Toronto Rehabilitation Institute - University Health Network, 520 Sutherland Drive, Toronto, Ontario M4G 3V9, Canada; 2. Rehabilitation Engineering Laboratory - University Health Network

Neuromuscular electrical stimulation (NMES) is used in the neurorehabilitation of people with neurological disorders such as spinal cord injury. There are two methods to evoke muscle contraction via NMES including peripheral nerve stimulation (PNS) or motor point stimulation (MPS), delivered to the so-named motor points located at neuromuscular junctions. We hypothesized that, based on the specific location of neuromuscular junctions and the distribution of muscle spindles that PNS and MPS would differ in their activation of sensory and motor axons. The study aimed to demonstrate the preferential activation of motor axons by MPS through neuro-electrophysiological examinations including pair-wised stimulations of PNS and MPS. We found: (1) PNS and MPS showed different patterns of motor and sensory recruitment curves (2) PNS and MPS differed in their ability to modify spinal circuits of agonist and antagonistic muscles. These results suggest that distinct differences exist in the motor and sensory recruitment by PNS and MPS, in that MPS preferentially activates motor axons. Our findings will help to deepen the current understanding of the neurophysiology of NMES and hence will contribute to the improvement of therapies using NMES.