Self-experienced acute pain refers to the unpleasant sensory and emotional experience related to tissue damage on one's own body. Self-pain perception evokes increased pain sensitivity and withdrawal urges from the pain-inducing stimulus. Previous studies revealed that vicarious pain could activate the behavioural defence system, which may result in the decrease in self-pain tolerance and increased self-pain intensity and unpleasantness ratings in the observer. The vicarious pain can reduce or enhance self- pain perception, but the factors that illustrate the direction of such effects are not fully understood yet. Terrighena EL et al. conducted the current study to determine the impact of vicarious pain on activation of behavioural defence systems and stimulation of withdrawal or appetitive systems that increases pain sensitivity.

A mixed factorial design with the between-subject factors exposure time (subliminal vs optimal) and vicarious pain (pain vs no pain images), and the within-subject factor session (baseline vs trial) was employed to evaluate the effect of visual awareness of vicarious pain images on subsequent self-pain in the cold-pressor test. A total of 77 healthy participants were enrolled in the study and self-pain tolerance, intensity and unpleasantness were studied in these patients.

The results of the study indicated significant interactions of exposure time and vicarious pain in all three dependent measures. A comparative analysis of vicarious pain and no-pain shows an increase in overall self-pain sensitivity with a reduction of pain tolerance and enhanced ratings of pain intensity and unpleasantness in the presence of visual awareness (optimal condition). Contrarily, in the absence of visual awareness (subliminal condition), a decrease in self-pain intensity and unpleasantness and no change in pain tolerance was obtained.

It was concluded from the study that the activation of defence mechanisms elicited by vicarious pain is dependent on relatively elaborate cognitive processes whereas activation of the appetitive system is obtained by highly automative manner independent from stimulus awareness. Such mechanisms may have evolved to facilitate empathic, protective approach responses toward suffering individuals, ensuring the survival of the protective social group.