Could placebo or nocebo effect influence implicit motor learning?

Abstract This study investigates the impact of placebo and nocebo effects on implicit motor learning and explores associated neurophysiological changes in the primary motor cortex (M1), using a neuromodulation technique (PAS protocol). Participants performed a probabilistic Serial Reaction Time Task (SRTT), which involved a numerical sequence created according to statistical regularities (SOC1, probable sequence), interspersed with a confounding sequence (SOC2), under three conditions: control (no manipulation), placebo (believing sham tDCS enhances performance), and nocebo (believing the opposite). Behavioral results show that the magnitude (i.e., ∆ Reaction Time) of implicit learning was greater when nocebo manipulations was applied compared to control and placebo conditions. Neurophysiological measures revealed that only nocebo manipulation that was able to modulate cortical activity by influencing LTP-like plasticity in M1. This paradoxical effect may stem from the suggestion that a negative effect, induced by nocebo manipulation, may have triggered compensatory mechanisms, ultimately improving performance.