Placebo and Nocebo Effects on Cognition: Mechanisms, Mediators, and Cognitive Resource Constraints.

Placebo and nocebo effects are well established in domains such as pain and motor performance; however, their impact on cognitive functioning remains a matter of debate. This narrative review provides a state of the art on placebo and nocebo research across different cognitive domains, identifies major methodological limitations and gaps in the literature, and proposes new hypotheses to guide future research. Given the limited number of studies and the heterogeneity in experimental paradigms, cognitive outcomes, and procedures, the available evidence supports only preliminary conclusions. Some studies suggest that reward-based learning and emotional processing may be susceptible to placebo and nocebo manipulations, whereas evidence concerning memory, attention, and working memory is limited and inconclusive. Building on this synthesis, we propose that factors such as outcome measures, task-specific features, and intervention type may modulate these effects. We also hypothesize that placebo/nocebo interventions, operating through implicit (e.g., conditioning) or explicit (e.g., verbal instructions) mechanisms, may influence cognitive performance differently depending on whether expectations target cognition directly or indirectly. These hypotheses remain to be tested using controlled and directly comparable experimental designs. By highlighting gaps in the literature, this review aims to stimulate future research establishing whether placebo and nocebo effects can be reliably elicited in specific cognitive functions and clarifying how and to what extent different procedures can influence them. These lines of research could have long-term translational implications, ultimately improving the effectiveness of neuropsychological interventions and cognitive training programs that leverage positive beliefs and mitigate negative expectations.