Beware of What You Expect? A Partial Replication Study on the Behavioral and Psychophysiological Effects of Negative Expectations on Mechanical Hypersensitivity.

Mechanical hypersensitivity of uninjured skin surrounding a cutaneous injury is a sign of plasticity of the nociceptive system and can be induced in healthy individuals using high-frequency electrical stimulation (HFS). However, despite a broad body of evidence for acute painful stimuli, mixed results have been reported concerning the role of negative expectations in the development of mechanical hypersensitivity. Given the theoretical and clinical relevance of verbal suggestions' impact on the potential development of mechanical hypersensitivity, this study aimed to replicate previous positive findings and establish the effects of negative expectations and HFS on autonomic activity. Sixty participants were randomly assigned to a nocebo or control group, with high-frequency stimulation (HFS) administered to one forearm. Negative expectations were induced only in the nocebo group through written instructions. We assessed the perceived intensity and spatial extent of mechanical hypersensitivity, as well as resting and pinprick-evoked pupil dilation as proxies for tonic arousal and phasic locus coeruleus activity, respectively. No statistically significant group differences were found in mechanical hypersensitivity, its spatial spread, or resting pupil dilation. Pinprick-evoked pupil dilation in the area of mechanical hypersensitivity increased after HFS, but this effect emerged only when a less conservative preprocessing approach was used. Manipulation checks further indicated that some control participants formed negative expectations. Under the present experimental conditions, our results do not support the possibility that negative expectations worsen the development of mechanical sensitivity or increase autonomic responses.