Abstract
Observing pain in others can enhance our own pain. Two aspects of this effect remain unknown or controversial: first, whether it depends on the ‘painfulness’ of the visual stimulus; second, whether it reflects a genuine bias in perception or rather a bias in the memory encoding of the percept. Pain ratings and vegetative skin responses were recorded while 21 healthy volunteers received electric nociceptive shocks under three experimental conditions: (i) observing a painful contact between the body and a harmful object; (ii) observing a non-painful body contact, (iii) observing a control scene where the body and the object are not in contact. Pain reports and vegetative responses were enhanced exclusively when the subjects observed a painful body contact. The effect on perception was immediate, abated 3 sec after the shock, and positively correlated with the magnitude of vegetative arousal. This suggests that (a) hyperalgesia during observation of painful scenes was induced by their pain-related nature, and not by the simple body contact, and (b) hyperalgesia emerged from a very rapid bias in the perceptual encoding of the stimulus, and was not the result of a retrospective bias in memory recollection. Observing pain-depicting scenes can modify the processing of concomitant somatic stimuli, increasing their arousal value and shifting perception toward more painful levels.
Highlights
Observing pain in others can enhance our own pain
A two-way analysis of variance (ANOVA) was performed on pain ratings with “image type” [Pain (P) vs. No-Pain (NP) vs. No-Contact (NC)] and “block type” [immediate 1 (IR_1) vs immediate 2 (IR_2) vs delayed (DR)] as factors (Fig. 1)
ANOVA analysis showed a significant effect of image type on the pain ratings to electrical shocks (F(2,20) = 15.1; p < 0.001), a significant effect of block type (F(2,20) = 23.2; p < 0.001), and a significant image * block type interaction (F(2;20) = 4.09; p = 0.003) (Fig. 1)
Summary
Observing pain in others can enhance our own pain. Two aspects of this effect remain unknown or controversial: first, whether it depends on the ‘painfulness’ of the visual stimulus; second, whether it reflects a genuine bias in perception or rather a bias in the memory encoding of the percept. The effect on perception was immediate, abated 3 sec after the shock, and positively correlated with the magnitude of vegetative arousal This suggests that (a) hyperalgesia during observation of painful scenes was induced by their pain-related nature, and not by the simple body contact, and (b) hyperalgesia emerged from a very rapid bias in the perceptual encoding of the stimulus, and was not the result of a retrospective bias in memory recollection. Such vegetative reactions are objective signals that co-vary with both subjective pain perception and brain activity[9,10], and represent reliable indexes of arousal that the subject cannot manipulate voluntarily[8,9] Enhancement of these autonomic responses has been reported during observation of other’s pain[11,12,13], and was found to be correlated with the ability to develop empathic behaviour[11]. We compared changes in pain ratings reported either immediately or several seconds following stimulus presentation
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