Dissociation and heterogeneity in high hypnotic suggestibility

Sammanfattning: Individuals who exhibit high hypnotic suggestibility are a heterogeneous population. Although they display uniformity on standard measures of hypnotic suggestibility, such individuals have been repeatedly found to display marked differences in a variety of dimensions of hypnotic responding, in their cognitive and experiential response to a hypnotic induction, and in different cognitive functions germane to hypnotic responding. There is considerable disagreement over how heterogeneity in this population is best explained, with componential models maintaining that highly suggestible individuals are a uniform population and typological models proposing that they consist of discrete subtypes. This dissertation describes four studies that tested predictions derived from dissociative typological models, which argue that highly suggestible individuals are comprised of one subtype characterized by a greater propensity for dissociation and a second subtype with superior imagery. Paper I used latent profile analysis to derive discrete profiles of participants on the basis of their spontaneous experiential responses to a hypnotic induction. This analysis yielded evidence for two subtypes of highly suggestible individuals, those who experienced greater distortions in awareness and volition and those with greater endogenously-directed attention and more vivid imagery. Paper II applied the dissociative typological models to individual differences in hypnotic responding, cognitive functioning, and psychopathology among HS individuals. High dissociative highly suggestible participants were more responsive to hallucination suggestions, experienced greater involuntariness during hypnotic responding, and displayed impaired working memory capacity and a greater predisposition to psychopathology, whereas low dissociative highly suggestible participants exhibited superior object visual imagery. Paper III tested the prediction that hypnosis differentially impacts cognitive control in the two subtypes. A hypnotic induction was found to marginally facilitate cognitive control in low suggestible and low dissociative highly suggestible participants but to deleteriously affect cognitive control in high dissociative highly suggestible participants. Paper IV examined the influence of a hypnotic induction on resting state functional connectivity and state dissociation in the same three groups. Counter to the typological models, but in support of the componential model, the two highly suggestible subtypes displayed uniform experiential and neurophysiological response patterns across control and hypnosis conditions. Both low and highly suggestible participants experienced increased state dissociation and exhibited reduced functional connectivity, particularly over anterior cortical regions during hypnosis but these effects were more pronounced in the latter group. The results of Papers I through III provide robust support for dissociative typological models, whereas those of Paper IV are inconsistent with these models. I conclude by considering how the divergent results can be reconciled and outline different ways of further discriminating between possible models of heterogeneity. Dissociative tendencies appear to play a fundamental role in modulating individual differences in high hypnotic suggestibility and should be afforded greater attention in future research on heterogeneity in this population.