The Effects of Tonic and Burst Spinal Cord Stimulation on Cortical Pain Processing and Their Interaction With...

Spinal cord stimulation (SCS) is an effective treatment for certain chronic pain conditions. Proposed mechanisms of SCS include modulation of the ascending lateral, ascending medial, and descending pain pathways. Conditioned pain modulation (CPM) evaluates the descending pathway by measuring ways a first painful stimulus is affected by a second painful stimulus.

We aim to increase insight into SCS mechanisms by exploring cortical activity in response to painful stimuli under various SCS paradigms and assessing how these responses are influenced by CPM.

21 patients with persistent spinal pain syndrome type 2 treated with SCS underwent three sessions (under tonic, burst, and sham SCS) with a one-week interval. Using magnetoencephalography, we measured the cortical responses to painful electrical stimuli before, during, and afterCPM. Cortical activity was analyzed in the time domain (evoked response) and time-frequency domain (beta event-related synchronization [ERS]).

Data from 14 patients qualified for analysis. Before CPM, the lowest amplitude of evoked responses occurred under tonic SCS, followed by sham SCS (p > 0.05). The lowest power of beta ERS occurred under sham SCS (p > 0.05). Pain ratings of the stimuli were statistically significantly reduced during CPM (p < 0.05). The amplitude of evoked responses was statistically significantly reduced in multiple regions during CPM under sham and burst SCS (p < 0.05). The power of beta ERS was reduced during CPM under tonic and burst SCS, whereas no reduction was observed under sham SCS (p > 0.05).

This exploratory study indicates that evoked and induced cortical responses reflect distinct mechanisms during CPM under SCS. Evoked responses, which primarily reflect bottom-up sensory processing, may be reduced by tonic SCS in the ascending lateral pathway areas before CPM. This reduction may suggest that tonic SCS suppresses input of the ascending lateral pathway, limiting additional inhibition by CPM. Beta ERS (induced response), which primarily reflects top-down modulation, decreased during CPM under tonic and burst SCS, suggesting engagement of the descending pain pathway.