Hypnotic Suggestions May Reduce The Conflict Between The Automatic And The Intentional Processes. Behavioral And Neurophysiological Evidence From The Stroop Task. Rinaldo Livio Perri , Valentina Bianco; Enrico Facco; Francesco Di Russo (Rome, Italy) C21
Introduction: A compelling literature suggested the possibility of adopting hypnotic suggestions to override the Stroop interference effect (i.e., slow speed and low accuracy in naming the ink color of an incongruent color word) among individuals with high level of hypnotizability (High). However, despite some studies corroborated these findings, others failed to replicate them, while only a few works attempted to provide a neurophysiological explanation of the effects, and none tested the role of different hypnotic suggestions. Also, the question of whether these effects are specific for Highs or common to Mediums as well is still open. Methods: Seventeen healthy volunteers participated in the study. Participation in the experiment consisted of three sessions: in the first one, the individual level of hypnotic susceptibility was assessed; in the second and third sessions, EEG activity was recorded while subjects performed the manual Stroop task in the baseline and hypnotic condition with perceptual (i.e., to focus only on the central letter of the words) and semantic suggestion (i.e., to see meaningless symbols), provided in a counterbalanced order. Results: The two hypnotic conditions did not affect the response speed on the Stroop task, but significantly increased the response accuracy regardless of the adopted suggestion. As for the brain activity, event-related potentials (ERP) analysis revealed common and specific effects for the two hypnotic suggestions. In particular, both types of suggestions increased the sensory awareness (the anterior pN1 component) and reduced the discriminative visual attention on the stimuli (the occipital N1 component) compared to the baseline condition. Moreover, the perceptual suggestion selectively engaged more executive control of the prefrontal cortex (the pre-stimulus pN component), while the semantic one selectively suppressed the P180 component whose neural source was identified in the left temporal cortex devoted to the graphemic analysis of the words. Conclusions: Present findings demonstrated that the perceptual and the semantic hypnotic suggestions reduced the Stroop errors, and that this effect is mediated by common and specific top-down modulation of different decision-making processes ranging from the expectancy stage to the pre-semantic processing of the words. Finally, as we recruited participants with a medium level of hypnotizability, present findings might be considered as potentially representative of the majority of the population.