Abstract
Compelling literature has suggested the possibility of adopting hypnotic suggestions to override the Stroop interference effect. However, most of these studies mainly reported behavioral data and were conducted on highly hypnotizable individuals. Thus, the question of the neural locus of the effects and their generalizability remains open. In the present study, we used the Stroop task in a within-subject design to test the neurocognitive effects of two hypnotic suggestions: the perceptual request to focus only on the central letter of the words and the semantic request to observe meaningless symbols. Behavioral results indicated that the two types of suggestions did not alter response time (RT), but both favored more accurate performance compared to the control condition. Both types of suggestions increased sensory awareness and reduced discriminative visual attention, but the perceptual request selectively engaged more executive control of the prefrontal cortex (PFC), and the semantic request selectively suppressed the temporal cortex activity devoted to graphemic analysis of the words. The present findings demonstrated that the perceptual and the semantic hypnotic suggestions reduced Stroop errors through common and specific top-down modulations of different neurocognitive processes but left the semantic activation unaltered. Finally, as we also recruited participants with a medium level of hypnotizability, the present data might be considered potentially representative of the majority of the population.
Highlights
The American Psychological Association (APA) defined hypnosis as “a state of consciousness involving focused attention and reduced peripheral awareness characterized by an enhanced capacity for response to suggestion” (Elkins et al, 2015)
Analysis of the response time (RT) showed a significant main effect of category (F2,32 = 37.17, p < 0.001; η2p = 0.69), and post hoc comparisons confirmed the known increase in RT for incongruent trials [652 ± 12 ms; 95% confidence interval (CI) = 612–692 ms] when compared to congruent (578 ± 10 ms; 95% CI = 547–608 ms; p < 0.001) and neutral trials (579 ± 9 ms; 95% CI = 552–606 ms; p < 0.001), whereas none of the other effects and interactions reached significant values
The perceptual suggestion to focus only on the central letter recruited more executive control of the prefrontal cortex (PFC) during the preparation stage, whereas the semantic suggestion to observe letters as meaningless symbols affected the graphemic analysis of the words by deactivating the left temporal cortex
Summary
The American Psychological Association (APA) defined hypnosis as “a state of consciousness involving focused attention and reduced peripheral awareness characterized by an enhanced capacity for response to suggestion” (Elkins et al, 2015). Stroop Task and Hypnotic Suggestions in hypnosis and hypnotic suggestions (for reviews, see Gruzelier, 1998; Vanhaudenhuyse et al, 2014), being this topic very important to understand brain mechanisms involved in attention and motor control (for a review, see Oakley and Halligan, 2013) Among these studies, there is a promising field suggesting the possibility of reducing automatic cognitive processes through hypnosis (for a review, see Lifshitz et al, 2013). The results were interpreted in terms of a functional dissociation of conflict monitoring and cognitive control processes in highs
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