Objective: To investigate the effects of placebo and paranormal belief on the laterality of pain perception.
Background: The right hemisphere is dominantly involved in both the mediation of pain sensation and the belief in paranormal phenomena. We set out to assess a possible influence of long-term belief systems on placebo analgesia in response to unilateral nociceptive stimuli.
Method: Forty healthy participants (20 high and 20 low believers as indexed by the Magical Ideation Scale) underwent a placebo analgesia study measuring stimulus detection, pain threshold, and pain tolerance by electrostimulation on the right and left hand. Placebo treatment consisted of the application of a sham cream on the hands.
Results: Placebo had a positive influence on pain perception in the 3 variables. Enhanced pain sensitivity for the left side was only found for the disbelievers. Placebo treatment resulted in a double dissociation: in believers, it increased tolerance exclusively on the left side, in disbelievers on the right side.
Conclusions: Our results confirm laterality effects in pain perception. However, only disbelievers conformed to the expected higher left-sided sensitivity. Placebo effects were dissociated between believers and disbelievers suggesting that short-term reactions to a placebo are modulated by a person's long-term belief system.
Department of Neurology, Neuropsychology Unit, University of Zürich, Zürich, Switzerland
Reprints: Caroline Klemenz, MSc, Department of Neurology, Neuropsychology Unit, University Hospital Zürich, Frauenklinikstr, 26, CH-8091 Zürich, Switzerland (e-mail: firstname.lastname@example.org).
Received for publication May 7, 2008; accepted April 19, 2009