Introduction: Chronic pain is one of the biggest problems within the healthcare system due to an increasing prevalence and socio-economic burden. A lack of understanding of the neurobiology of chronic pain implies the use of different treatment technologies, where the effect of their use is not clear. Special emphasis is placed on the technologies aimed at studies of CNS changes (Central sensitization, homeostatic plasticity) associated with chronic pain. This project has targeted evaluation of the effect when using HD-tDCS in relation to the study of cortico motor homeostasis in M1 and of interactions between cortical and spinal pain modulating mechanisms.

Method: A randomized placebo-controlled crossover experiment in two sessions with 10 healthy subjects. The sessions were identical and consisted of baseline measurements of spinal and cortical response (CPM/TSP/pPDT and MEPs), experimental pain induction (Capsaicin) or placebo, measurements of spinal and cortical response after pain induction (CPM/TSP/pPDT and MEPs) , HD-tDCS with the aim of inducing HP and measurements of spinal and cortical response (CPM/TSP/pPDT and MEPs) after the application of HD-tDCS.

Results: A significant reduction of CPM magnitude in the Placebo group (p=0.003) after HD-tDCS applied for 7 and 5 min with a 3-min interval in between. No statistically significant difference in TSP/pPDT magnitude and in MEPs amplitude in both groups.

Conclusion: This study is the first investigation of homeostatic plasticity and psychophysical paradigms measured by Cuff algometry underlying the central pro- and anti-nociceptive pain modulation. Data show a reduction of antinociceptive pain modulation (CPM) in response to HP induction in pain-free subjects. These data expand the understanding of pathophysiological mechanisms of the central pain modulation.