Possible role of the Gray's behavioral inhibition system in the greater efficacy of pleasant than unpleasant imagery in subjects with high hypnotizability

The aim of the study was to investigate the subjective experience and the autonomic correlates of the imagery of a painful (Pain) and of a pleasant tactile stimulation of one hand (PT) in subjects with high(highs) and low (lows) hypnotizability. The guided imagery of pain described a cold pressor test physically experienced by participants two days earlier, and the tactile imagery described a pleasant contact with soft fabrics. Highs were characterized by higher absorption (Tellegen Absorp-tion Scale, TAS), better visual and cutaneous imagery abilities (Betts questionnaire), greater proneness to inhibit possibly stressful/painful experience/behavior (Behavioral/Inhibition Systems, BIS/BAS) than lows, while anxiety levels were similar in the two groups. Self-reports of the perceived pain intensity and of the vividness of the perception of pleasant tactile stimulation, mean RR (=1/heart rate), heart rate variability (standard deviation, SD; respiratory-related root mean square successive difference, RMSSD), mean skin blood flow (SBF) and tonic skin conductance (SC) were recorded. Highs reported better imagery than lows for the imagery of pleasant touch, but not for the painful imagery. No correlation between the reported efficacies of the two imageries was observed inboth groups. TAS scores significantly correlated with the experience of pleasant touch, but not with the perceived pain. RR did not change during both cognitive tasks in highs and during Pain in lows, while it increased in lows during the imagery of pleasant touch; SD and RMSSD decreased during both tasks with respect to basal conditions. SBF decreased more during the painful than the pleasant imagery inboth groups and became higher in lows than in highs throughout both tasks. The absence of significant correlation between the reported efficacies of the two imageries suggests that different mechanisms may be responsible for them. Indeed, higher scores of absorption account for higher efficacy of the imagery of pleasant touch, but not for pain perception during pain imagery. The reduction of heart rate variability and the increase in tonic skin conductance during imagery indicate that both groups did become engage either in the pleasant or in the painful task. However, the lower levels of skin blood flow observed in highs with respect to lows suggest that the highs' engagement in the tasks may have been deeper than the lows. Since highs had higher imagery/absorption abilities than lows but were more successful only in the pleasant imagery, our findings suggest that imagery abilities are not sufficient to enhance the likelihood o fre-experiencing past painful events and, thus, the likelihood of a shift from acute to chronic pain in highs. Indeed, Gray's behavioral inhibition system could have a role in the hypnotizability-related pain coping and induce highs to dissociate from painful mental images. In conclusion,the Theory of Threat Perception should be revisited in order to interpret the prevalence of highs among chronic pain patients. In addition,further investigation could show whether the BIS/BAS systems may account also for part of the effects of the suggestions of analgesia and for placebo responses in the general population.