To investigate the effects of placebo and paranormal belief on the laterality of pain perception.
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.
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.
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.
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