Placebos can change affective contexts: An event-related potential study

An unpleasant context (bitter aftertaste) is able to reduce the late positive potential (LPP) elicited by affective pictures. This study attempted to influence this context with a placebo. Sixty-eight women were randomly assigned to three groups: Water, Bitter/No-Placebo, Bitter/Placebo. Participants in the 'bitter groups' first rinsed their mouth with wormwood tea that caused a bitter aftertaste. Subsequently, the placebo group received sham light therapy on the tongue to 'reduce the sensitivity of the taste buds'. All groups viewed disgusting and non-disgusting pictures while their electroencephalogram was recorded. The Bitter/Placebo group reported reduced bitterness and disgust for the aftertaste after the sham treatment. The LPP reduction (300 - 600 ms after picture onset) associated with the bitter aftertaste (as shown by the Bitter/No-Placebo group) was attenuated due to the placebo treatment. This is the first EEG study to demonstrate that a context-targeting placebo is able to change automatic attention allocation.