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.
Keywords: Migraine, Laser Enoked potentials, suggestion, LEP, MIDAS, Visual analogue scale, Electro-oculogram, Anxiety, Depression, ANOVA, Anterior cingulate cortex
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