Placebo and cognitive enhancement: the cognitive and neurological effects of conditioning and verbal suggestion

Previous research has shown that subjective cognitive performance can be enhanced, and that sense of agency can be lowered via verbal suggestion of brain stimulation. Mixed results have been found on the effect of placebo stimulation on error-related negativity (ERN) amplitude, which is an implicit outcome measure. This EEG study focused on the role of verbal suggestion and associative learning in eliciting placebo effects in subjective performance, sense of agency, and ERN amplitude. Using a within-subject design, we recorded EEG while participants (n = 19) performed in a simple cognitive task. Participants were told that a sham brain stimulation device would either enhance (placebo condition) or impair (nocebo condition) their cognitive performance. Next, we used a conditioning phase in which we altered the task difficulty according to the experimental block in order to induce the association between task difficulty and proposed stimulation. After this conditioning phase, the task...Show morePrevious research has shown that subjective cognitive performance can be enhanced, and that sense of agency can be lowered via verbal suggestion of brain stimulation. Mixed results have been found on the effect of placebo stimulation on error-related negativity (ERN) amplitude, which is an implicit outcome measure. This EEG study focused on the role of verbal suggestion and associative learning in eliciting placebo effects in subjective performance, sense of agency, and ERN amplitude. Using a within-subject design, we recorded EEG while participants (n = 19) performed in a simple cognitive task. Participants were told that a sham brain stimulation device would either enhance (placebo condition) or impair (nocebo condition) their cognitive performance. Next, we used a conditioning phase in which we altered the task difficulty according to the experimental block in order to induce the association between task difficulty and proposed stimulation. After this conditioning phase, the task difficulty was equal across conditions. We found increased subjective performance in the nocebo condition, but not the placebo condition, compared to control. We found a lower sense of agency in the placebo condition, but not the nocebo condition, compared to control. Finally, we found no difference in ERN amplitude throughout conditions. These results are not in line with previous research. Our conditioning phase did not work as intended and therefor the results are difficult to interpret. In addition, based on the results of our post-test questionnaire, our verbal suggestion might have been too weak. Future research should try to replicate the earlier results and continue investigating possible (other) implicit outcome measures.Show less

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Placebo and cognitive enhancement: the cognitive and neurological effects of conditioning and verbal suggestion