"That's not my arm": a hypnotic analogue of somatoparaphrenia

"Instrumental hypnosis" allows researchers to model clinical symptoms in the laboratory, creating "virtual patients" with reversible disturbances in, for example, perception, action, memory, or belief. We used hypnosis to temporarily recreate somatoparaphrenia, a delusional belief that one's own limb belongs to someone else.

We compared a "Fully Formed" somatoparaphrenia suggestion with a "Factor 1 + Factor 2" suggestion that attempted to generate the delusional belief from analogues of its hypothesised underlying factors (i.e., paralysis plus disrupted critical belief evaluation). We tested and then challenged subjects' responses to these suggestions.

Although many hypnotic subjects experienced temporary paralysis, only a minority claimed their arm did not belong to them. Notably, the Fully Formed suggestion was more successful in recreating features of somatoparaphrenia than the Factor 1 + Factor 2 suggestion. In response to the challenges, some of those who developed temporary somatoparaphrenia maintained their belief throughout the hypnosis session. CONCLUSIONS. We discuss these findings in terms of the "two-factor" theory of delusions and we highlight the advantages versus disadvantages of using hypnosis to explore such delusional beliefs in the laboratory.