Sub-optimal presentation of painful facial expressions enhances readiness for action and pain perception following electrocutaneous stimulation

Abstract

Observation of others' painful facial expressions has been shown to facilitate behavioralresponse tendencies and to increase pain perception in the observer. However, inprevious studies, expressions were clearly visible to the observer and none of thosestudies investigated the effect of presence of peripheral stimulation on responsetendencies. This study focuses on the effect of sub-optimal presentation of painful facialexpressions in the presence and absence of an electrocutaneous stimulus. Twenty-twohealthy individuals categorized arrow targets which were preceded by a sub-optimallypresented facial expression (painful, happy, or neutral in different blocks). On half ofthe trials, aversive electrocutaneous stimulation was delivered to the wrist of the non-dominant hand between the presentation of facial expression and target (an arrowdirecting to right or left). Participants' task was to indicate direction of the arrow assoon as it appears on the screen by pressing the corresponding key on the keyboardand to rate their pain at the end of block. Analysis showed that responses were fasterto targets preceded by aversive stimulation than to targets not preceded by stimulation,especially following painful expressions. Painfulness ratings were higher followingpainful expressions than following happyexpressions. These findings suggest thatsub-optimally presented painful expressions can enhance readiness to act to neutral,non-pain-related targets after aversive stimulation and can increase pain perception.