Learning potentiates neurophysiological and behavioral placebo analgesic responses

expectation and conditioning are supposed to be the two main psychological mechanisms for inducing a placebo response. here, we further investigate the effects of both expectation, which was induced by verbal suggestion alone, and conditioning at the level of N1 and N2-P2 components of CO2 laser-evoked potentials (LEPs) and subjective pain reportss. forty-four healthy volunteers were pseudorandomly assigned to one of three experimental groups: group 1 was tested with verbal suggestion alone. group 2 was tested with a conditioning procedure, whereby the intensity of painful stimulation was reduced surreptitiously, so as to make the volunteers believe that the treatment was effective. group 3 was a control group that allowed us to rule out phenomena of sensitization and/or habituation. pain perception was assessed according to a numerical rating scale (NRS) ranging from 0 = no pain sensation to 10-maximum imaginable pain. both verbal suggestions (group 1) and ocnditioning (group 2) modified the N2 P2 complex, but not the N1 component of LEPs. however, the suggestion-induced LEP changes occured without subjective perception of pain decrease. conversely, the N2 P2 amplitude changes that were induced by the conditioning procedure were associated with the subjective perception of pain reduction. compared to natural history, conditioning produced more robust reductions of LEP amplitudes than verbal suggestions alone. overall, these findings indiate that prior positive experience plays a key role in maximizing affects the early central nocicecptive preocessing. (C) 2008 International association for the study of pain.