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.