Highlights
- •Observing pain in another induces endogenous analgesia.
- •Threat of pain to oneself also initiates endogenous analgesia.
- •Endogenous analgesia was observed in the absence of any somatosensory afferent input.
- •Threat cues may significantly influence test paradigms for endogenous analgesia.
Abstract
Many factors interact to influence threat perception and the subsequent experience
of pain. This study investigated the effect of observing pain (extrinsic threat) and
intrinsic threat of pain to oneself on pressure pain threshold (PPT). Forty socially
connected pairs of healthy volunteers were threat-primed and randomly allocated to
experimental or control roles. An experimental pain modulation paradigm was applied,
with non-nociceptive threat cues used as conditioning stimuli. In substudy 1, the
extrinsic threat to the experimental participant was observation of the control partner
in pain. The control participant underwent hand immersion in noxious and non-noxious
water baths in randomized order. Change in the observing participant's PPT from baseline
to mid- and postimmersion was calculated. A significant interaction was found for
PPT between conditions and test time (F2,78 = 24.9, P < .005). PPT increased by 23.6% ± 19.3% between baseline and during hand immersion
(F1,39 = 43.7, P < .005). Substudy 2 investigated threat of imminent pain to self. After a 15-minute
break, the experimental participant's PPT was retested (“baseline 2”). Threat was
primed by suggestion of whole arm immersion in an icier, larger water bath. PPT was
tested immediately before anticipated arm immersion, after which the experiment ended.
A significant increase in PPT between “baseline 2” and “pre-immersion” was seen (t = −7.6,
P = .005), a pain modulatory effect of 25.8 ± 20.7%. Extrinsic and intrinsic threat
of pain, in the absence of any afferent input therefore influences pain modulation.
This may need to be considered in studies that use noxious afferent input with populations
who show dysfunctional pain modulation.
Perspective
The effect on endogenous analgesia of observing another's pain and of threat of pain
to oneself was investigated. Extrinsic as well as intrinsic threat cues, in the absence
of any afferent input, increased pain thresholds, suggesting that mere threat of pain
may initiate analgesic effects in traditional noxious experimental paradigms.
Key words
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Article info
Publication history
Published online: November 27, 2017
Accepted:
November 9,
2017
Received in revised form:
October 20,
2017
Received:
August 27,
2017
Footnotes
All financial and material support was provided by the School of Physiotherapy, University of Notre Dame Australia.
The authors have no conflicts of interest to declare.
Identification
Copyright
© 2017 by the American Pain Society
