Placebo-suggestion modulates conflict resolution in the Stroop Task.

Here, we ask whether placebo-suggestion (without any form of hypnotic induction) can modulate the resolution of cognitive conflict. Naïve participants performed a Stroop Task while wearing an EEG cap described as a "brain wave" machine. In Experiment 1, participants were made to believe that the EEG cap would either enhance or decrease their color perception and performance on the Stroop task. In Experiment 2, participants were explicitly asked to imagine that their color perception and performance would be enhanced or decreased (non-hypnotic imaginative suggestion). We observed effects of placebo-suggestion on Stroop interference on accuracy: interference was decreased with positive suggestion and increased with negative suggestion compared to baseline. Intra-individual variability was also increased under negative suggestion compared to baseline. Compliance with the instruction to imagine a modulation of performance, on the other hand, did not influence accuracy and only had a negative impact on response latencies and on intra-individual variability, especially in the congruent condition of the Stroop Task. Taken together, these results demonstrate that expectations induced by a placebo-suggestion can modulate our ability to resolve cognitive conflict, either facilitating or impairing response accuracy depending on the suggestion's contents. Our results also demonstrate a dissociation between placebo-suggestion and non-hypnotic imaginative suggestion.

The neural correlates of intending not to do something.

There has been plenty of research concerning the representation of voluntary action in the human brain. However, the question of how we represent the voluntary omission of an action has been largely neglected. Therefore this study aimed at investigating the representation of intentionally not doing something by means of event-related potentials (ERPs). Free-choice nonactions elicit similar evoked potentials as free-choice actions and instructed actions (augmented P2 and attenuated N2), which leads us to assume that the voluntary intention, not the overt nonaction, is the characteristic feature of free-choice nonaction. Beyond that we reveal differences between free-choice nonactions and instructed nonactions that resemble the typical N2 and P3 augmentation usually seen for NoGo trials in Go/NoGo paradigms, with the difference that the free-choice nonaction ERP takes the place of the typical Go ERP.