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

Neuromuscular electrical stimulation (NMES) is used in the rehabilitation of people with neurological disorders. Two methods exist to evoke muscle contraction via NMES: peripheral nerve stimulation (PNS) and 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, PNS and MPS would differ in their activation of sensory and motor axons, and that MPS would produce strong antidromic activation. We demonstrated that (1) PNS and MPS differ in sensory and motor recruitment curve patterns (2) MPS cannot induce reciprocal inhibition, and (3) that MPS induces antidromic firing and strong recurrent inhibition of the SOL H-reflex. These results suggest that distinct differences exist in the recruitment patterns of PNS and MPS. Our findings contribute to the neurophysiological understanding of NMES and hence will improve NMES-based therapies in the future.