The study by Schabrun et al. published in Brain Stimulation 2014 is one of the most interesting papers I have read last year. This might be due to the fact that I am not at all an expert in neuromodulation, but even so the study is highly innovative and has amazing findings. The paper reports a placebo-controlled cross-over study investigating the effect of transcranial direct current stimulation (tDCS) combined with peripheral electrical stimulation (PES) treatment on pain, cortical organization, sensitization and sensory function in 16 patients with chronic low back pain. It was found that a combined tDCS/PES intervention is more effective for improving not only chronic low back pain symptoms, but also for improving the mechanisms of cortical organization and central sensitization than either intervention applied alone or a sham control.
More and more clinicians and researchers agree that pain therapy should target the central nervous system rather than peripheral structures. tDCS is a treatment that targets the brain directly by using electrical current delivered through electrodes (anode and cathode) places on the head to induce a weak electrical field in the brain to change the action potential threshold. The latter implies either membrane potential de- or hyperpolarisation. Are you lost? No worries, it means that tDCS changes the excitability of brain circuitries. If only it could decrease the excitability of the pain matrix … However up to now the results from tDCS studies in chronic pain patients have been rather disappointing, with small effect sizes and short-term effect.
This new study from Paul Hodges’ group suggests that the effects of tDCS (applied to the motor cortex) may be enhanced (a ‘priming’ effect) by the simultaneous application of PES (transcutaneous electrical nerve stimulation if you which). The authors speculate on the exact mechanism of action: PES reduces corticospinal excitability by means of long-term depression. This should make neural networks more susceptible to the depolarization currents of anodal tDCS. In this study, the combined treatment lead to marked improvements in various measures of central sensitization, including pain sensitivity. As such, it adds significantly to the ongoing discussion regarding treatment strategies for central sensitization pain.