Neuromodulation of conditioned placebo/nocebo in heat pain: anodal vs cathodal transcranial direct current stimulation to the right dorsolateral prefrontal cortex.

Placebo and nocebo play an important role in clinical practice and medical research. Modulating placebo/nocebo responses using noninvasive brain stimulation methods, such as transcranial direct current stimulation (tDCS), has the potential to harness these effects to therapeutic benefit in a clinical setting. In the present study we assessed the effect of anodal and cathodal tDCS over the right DLPFC on conditioned placebo/nocebo cue response to heat pain. Two matched groups of healthy volunteers were subjected to an identical session of conditioning, during which low and high cues (abstract images) were associated with low and high pain levels, respectively. Twenty-minute 2mA tDCS (either anodal or cathodal) over the right DLPFC was applied. The influence of tDCS current polarity (anodal vs. cathodal) on placebo and nocebo was assessed, using subjects’ pain ratings in response to identical pain preceded by the conditioned high or low cues. The duration of cue presentation varied to allow either fully conscious or subliminal processing. Significant placebo and nocebo effects in the anodal but not the cathodal group were elicited with the conditioning paradigm. This study provides evidence of a possibility to modulate the conditioned placebo and nocebo effect by changing the excitability of the right DLPFC using tDCS.