In the general population, transcranial anodal direct current stimulation of the cerebellum (ctDCS) reduces pain intensity and the amplitude of nociceptive laser evoked potentials (LEPs), whereas cathodal ctDCS elicits opposite effects. Since behavioral findings suggest that the cerebellar activity of highly hypnotizable individuals (highs) differs from the general population, we investigated whether hypnotizability-related differences occur in the modulation of pain by ctDCS. Sixteen healthy highs (according to the Stanford Hypnotic Susceptibility Scale, form A) and 16 participants not selected according to hypnotizability (controls) volunteered to undergo laser nociceptive stimulation of the dorsum of the left hand before and after anodal or cathodal ctDCS. LEPs amplitudes and latencies and the subjective pain experience (Numerical Rating Scale) were analyzed. Smaller LEP amplitudes and longer latencies were observed in highs with respect to controls independently of stimulation. After anodal and cathodal cerebellar stimulation, controls reported lower and higher pain than before it, respectively. In contrast, highs did not report significant changes in the perceived pain after both stimulations. They increased significantly their N2/P2 amplitude after anodal ctDCS and did not exhibit any significant change after cathodal tDCS, whereas controls decreased the N1 and N2P2 amplitude and increased their latency after anodal cerebellar stimulation and did the opposite after cathodal ctDCS. In conclusion, the study showed impaired cerebellar pain modulation and suggested altered cerebral cortical representation of pain in subjects with high hypnotizability scores.
Keywords: Cerebellum; Hypnotizability; Laser evoked potentials; Pain; Transcranial direct current stimulation.