Itch evoked by the rubber hand illusion

It has been well-established that expectancies can influence itch intensity. It remains to be established whether psychological processes can lead to non-itchy input being perceived as itchy. The current study aimed to investigate whether healthy individuals perceive non-itchy tactile stimulation (rubbing) as itchy when having the illusion that an itch stimulus is applied (using the rubber hand illusion; RHI). Moreover, it was investigated whether this effect depended on psychological characteristics, including expectancies. In 36 healthy female volunteers, ownership over the rubber arm was induced in a standard RHI setup. After assessing the itch-inducing properties of merely rubbing, baseline itch was evoked by rubbing cowhage spicules (pruritogenic tropical bean particles) onto the left forearm. Cowhage was kept on the arm for some minutes (follow-up phase). Similarly, cowhage was subsequently applied onto the rubber arm, while the participant’s concealed right arm was simultaneously rubbed without cowhage. Mean (mean=0.8, SD=1.1) and peak itch (mean=1.3, SD=1.4) significantly differed from zero (t=5.74, p<0.001 and t=6.89, p<0.001, respectively). Expectations did not mediate the effect, but self-reported attention to itch (PVAQ-itch) was positively associated with itch during follow-up. Low levels of itch were induced using the RHI paradigm, demonstrating the role of psychological factors in itch perception.