This paper has been accepted in the Journal of Alternative and Complementary Medicine and will be published later in the year:
Models of the placebo effect: Investigating a possible retrocausal factor
Objective: Conventional models of placebo effects assume that all mind/body responses associated with expectation can be explained by ordinary causal processes. This experiment tested whether some placebo effects may also involve retrocausal, or time-reversed, influences.
Design: Slow cortical potentials in the brain were monitored while adult volunteers anticipated either a flash of light or no flash, selected with equal probability by a noise-based random number generator. Data were collected in individual sessions of 100 trials, contributed by 13 female and 7 male adult participants.
Outcome measures: Ensemble median slow cortical potentials one second prior to a light flash were compared with the same measures prior to no flash. A nonparametric randomized permutation technique was used to statistically assess the observed difference. EEG data were analyzed separately by gender.
Results: Females’ slow cortical potentials significantly differentiated before stimulus onset (z = 2.72, p = 0.007, two-tailed), and males showed a suggestive effect in the opposite direction (z = -1.64, p = 0.10, two-tailed). Examination of alternative explanations indicated that these effects were not due to anticipatory strategies, equipment or environmental artifacts, or violation of statistical assumptions.
Conclusions: This experiment, in light of previous studies showing similar, unconscious “presentiment” effects in humans, suggests that comprehensive models seeking to explain placebo effects, and in general how expectation affects the mind and body, may require serious consideration of transtemporal or retrocausal factors.