Mechanisms of Dorsal Root Ganglion Stimulation in Pain Suppression: A Computational Modeling Analysis.

ABSTRACT

OBJECTIVE: The mechanisms of dorsal root ganglion (DRG) stimulation for chronic pain remain unclear. The objective of this work was to explore the neurophysiological effects of DRG stimulation using computational modeling. METHODS: Electrical fields produced during DRG stimulation were calculated with finite element models, and were coupled to a validated biophysical model of a C-type primary sensory neuron. Intrinsic neuronal activity was introduced as a 4 Hz afferent signal or somatic ectopic firing. The transmembrane potential was measured along the neuron to determine the effect of stimulation on intrinsic activity across stimulation parameters, cell location/orientation, and membrane properties. RESULTS: The model was validated by showing close correspondence in action potential (AP) characteristics and firing patterns when compared to experimental measurements. Subsequently, the model output demonstrated that T-junction filtering was amplified with DRG stimulation, thereby blocking afferent signaling, with cathodic stimulation at amplitudes of 2.8-5.5 × stimulation threshold and frequencies above 2 Hz. This amplified filtering was dependent on the presence of calcium and calcium-dependent small-conductance potassium channels, which produced a hyperpolarization offset in the soma, stem, and T-junction with repeated somatic APs during stimulation. Additionally, DRG stimulation suppressed somatic ectopic activity by hyperpolarizing the soma with cathodic or anodic stimulation at amplitudes of 3-11 × threshold and frequencies above 2 Hz. These effects were dependent on the stem axon being relatively close to and oriented toward a stimulating contact. CONCLUSIONS: These results align with the working hypotheses on the mechanisms of DRG stimulation, and indicate the importance of stimulation amplitude, polarity, and cell location/orientation on neuronal responses.