A Simulation Study on Selective Stimulation of C-Fiber Nerves for Chronic Pain Relief

It has been reported that stimulating nociceptive unmyelinated C nerves ( C ) near the sarcolemma could induce the secretion of endogenous opioids that relieve chronic pain. However, a substantial concern remains: concomitant stimulation might cause acute pain to nociceptive myelinated \text{A}\delta nerves ( A\delta ), which generally have a lower activation threshold than the C . However, few studies have reported on C selectivity over A\delta ( C -selectivity). In this study, the C and A\delta nerves were modeled using the Hodgkin-Huxley (HH) and McIntyre-Richardson-Grill (MRG) models, respectively. Two potential stimulation schemes, including bipolar square waves and burst modulated alternating current, together with a new stimulation scheme named inhibit- A\delta (i- A\delta ) that inhibits the excitability of the A\delta , were systematically investigated. Their stimuli were given to the C and A\delta nerves through point electrodes located near the nerve fibers. Simulation results revealed that i- A\delta presented the highest C -selectivity, which provides a basis for non-invasive effective chronic-pain relief.