Burst and Tonic Spinal Cord Stimulation: Different and Common Brain Mechanisms.

OBJECTIVE Spinal cord stimulation is commonly used to treat medically intractable pain. Different stimulation designs are used to obtain pain suppression such as tonic stimulation, high frequency stimulation, and burst stimulation. Preliminary analysis of the same data used in this study demonstrated that burst stimulation likely modulates the medial pain pathways in contrast to tonic stimulation. The question arises what different and common supraspinal mechanisms burst and tonic stimulation use. MATERIALS AND METHODS The clinical and electroencephalography (EEG) data of five patients undergoing tonic, burst, and sham stimulation were analyzed to look at the commonalities and differences between burst and tonic stimulation. A source-localized (sLORETA) EEG substraction and conjunction analysis is performed in each condition for both activity and functional connectivity. A ratio between the dorsal anterior cingulate cortex (dACC) and pregenual anterior cingulate cortex/ventromedial prefrontal cortex (pgACC/vmPFC) is calculated to reflect a balance between pain supporting and pain suppressing systems. RESULTS Differences are noted in the dACC, dorsolateral prefrontal cortex, the primary somatosensory cortex, and the posterior cingulate cortex (PCC). Burst and tonic stimulation share activation in the pgACC, inferior parietal area, which encompasses the inferior secondary somatosensory cortex, PCC, and the parahippocampus. Burst suppression normalizes the pain supporting/pain suppressing balance in contrast to tonic stimulation. DISCUSSION AND CONCLUSION These data suggest that burst and tonic stimulation both modulate the descending pain inhibitory system (via pgACC), as well as a self-referential contextual (via PCC) aversive memory system (via parahippocampus). However, burst normalizes the pain supporting/suppressing balance in contrast to tonic mode by a greater effect on the dACC.