Belief and expectation are part of placebo effect.
Migraine patients are characterized by a dysfunctional modulation of
pain processing, though a clear placebo effect emerges in clinical trials. The aim of the study was to evaluate the effect of visual and verbal suggestion on subjective
pain sensation and cortical responses evoked by CO2 painful
laser stimuli in
migraine without aura patients vs healthy controls. Twenty-six patients were recorded during the inter-ictal phase and compared to 26 sex and age-matched controls. The right hand and the right supraorbital zone were stimulated during a not conditioned and a conditioned task, where
laser stimuli were delivered after a verbal and visual cues of decreased (D), increased (I) or basal (B) intensity, which was left unmodified during the entire task. In control subjects
pain rating changed, according to the announced intensity, while in
migraine patients the basal hyper-algesia remained unmodified. The N1 and N2 amplitudes tended to change coherently with the stimulus cue in controls, while an opposite paradoxical increase in decreasing condition emerged in
migraine. The P2 amplitude modulation was also reduced in
migraine, differently from controls. The altered pattern of
pain rating and N2 amplitude modulation concurred with frequency of
migraine, disability and
allodynia. In controls suggestion influenced cortical
pain processing and subjective
pain rating, while in
migraine a peculiar pattern of cortical activation contrasted external cues in order to maintain the basal hyper-algesia. This scarce influence of induced suggestion on
pain experience seemed to characterize patients with more severe
migraine and central sensitization.