Placebo analgesia as a case of a cognitive style driven by prior expectation

Placebo analgesia has been shown to be driven by expectations of treatment effects. We suggest that the expectation of treatment creates uncertainty about the sensory information of pain. We tested the hypothesis that in placebo responders uncertainty generated by expectations generalizes to other cognitive processes by recruiting participants for a placebo study who had previously taken part in a visual cue-picture decision making perceptual task. The task investigated how participants utilised prior cues against discrepant and uncertain sensory information. Participants were selected based on their degree of acquiescence in the cue-picture task. The placebo experiment was split into three blocks of pre-treatment, treatment and post-treatment. Participants were told that they may or may not receive an anaesthetic cream on one arm. However, all participants received inactive cream paired with non-painful stimuli during the treatment block. Electroencephalography (EEG) was used to measure pain evoked potentials to laser heat to determine if the behavioural misperception of pain translated into a physiological response. Regression models showed that both behavioural and physiological placebo responses could be predicted by participants' scores of acquiescence in the cue-picture decision making task. Placebo analgesia seems to be influenced by a cognitive style that assimilates responses to expectations increasing the chances of error when detecting discrepant sensory information.