Nocebo Hyperalgesia can be Induced by the Observation of a Model Showing Natural Pain Expressions.

OBJECTIVES

Nocebo hyperalgesia is an increase in pain through the expectation of such an increase as a consequence of a sham treatment. Nocebo hyperalgesia can be induced by observation of a model demonstrating increased pain via verbal pain ratings. The aim of the present study was to investigate whether observing natural pain behavior, such as facial pain expressions, can also induce nocebo responses.

MATERIALS AND METHODS

Eighty female participants (age: 22.4 y±4.8) underwent a pressure-pain procedure (algometer) on both hands and rated their pain on a numerical rating scale. All participants received ointment on one of their hands, but no explanation was given for this. Before their own participation, the participants watched a video in which a woman underwent the same procedure and who either modeled increased pressure pain upon ointment application (nocebo condition) or showed a neutral facial expression throughout (control condition).

RESULTS

A 2×2 analysis of variance with condition (nocebo; control) as a between-subjects factor and ointment application (with; without) as a within-subject factor revealed a main effect for ointment and a condition×ointment interaction. In the nocebo condition, pain ratings were higher with ointment than without.

DISCUSSION

For the first time, it was shown that watching a model demonstrating pain through facial expressions induced nocebo hyperalgesia. As we mostly express pain through natural pain behavior rather than through pain ratings, this paradigm extends our knowledge of observational learning about pain and may have implications for contexts in which persons watch others undergo painful procedures.