Subjects' hypnotizability level affects somatosensory evoked potentials to non-painful and painful stimuli

Objective: We evaluated the working hypothesis that the EEG activity associated to non-painful and painful stimuli in condition of waking state (no hypnotic procedure) was related to the hypnotizability level. Methods: Hypnotizability level was measured in 16 healthy subjects through the Italian version of the Stanford Hypnotic Susceptibility Scale (SHSS, score: 0-12). EEG data (56 electrodes) were recorded during non-painful and painful electrical stimuli applied to the left index finger. Cortical activity (vertex N1-P2 complex) was compared in subjects with low hypnotizability level (N = 8, SHSS:0-6) vs. subjects with high hypnotizability level (N = 8, SHSS:7-12). Results: The amplitude of the N1-P2 complex was lower in the High-hypnotizability compared to the Low-hypnotizability group over primary sensorimotor cortex (C3 and C4 electrodes) and centro-parietal midline areas (Cz and Pz electrodes) for non-painful and painful stimuli. The SHSS showed a statistically significant negative correlation with the vertex N1-P2 complex at C3 and Cz (r= -0.5, p< 0.05) electrodes for non-painful stimuli. Conclusion: Compared to the Low-hypnotizability subjects, High-hypnotizability subjects showed a reduced cortical activity related to non-painful and painful stimuli. Significance: The results suggest a relationship between hypnotizability and cortical activity related to non-painful and painful stimuli in the condition of waking state (no hypnotic effect).