Highlights
- •Classical conditioning could drive pain to persist after tissue has healed.
- •Neutral somatosensory stimuli could influence pain thresholds via conditioning.
- •This study tested for conditioned alterations of human pain thresholds to laser.
- •It used simultaneous pairing of non-noxious with noxious stimuli.
- •The results showed a classically conditioned change in human pain thresholds.
Abstract
A classical conditioning framework is often used for clinical reasoning about pain
that persists after tissue healing. However, experimental studies demonstrating classically
conditioned pain in humans are lacking. The current study tested whether non-nociceptive
somatosensory stimuli can come to modulate pain thresholds after being paired with
painful nociceptive stimuli in healthy humans. We used a differential simultaneous
conditioning paradigm in which one nonpainful vibrotactile conditioned stimulus (CS+) was simultaneously paired with an unconditioned painful laser stimulus, and another
vibrotactile stimulus (CS−) was paired with a nonpainful laser stimulus. After acquisition, at-pain-threshold
laser stimuli were delivered simultaneously with a CS+ or CS− vibrotactile stimulus. The primary outcome was the percentage of at-threshold laser
stimuli that were reported as painful. The results were as expected: after conditioning,
at-threshold laser trials paired with the CS+ were reported as painful more often, as more intense, and as more unpleasant than
those paired with the CS−. This study provides new evidence that pain thresholds can be modulated via classical
conditioning, even when the stimulus used to test the threshold cannot be anticipated.
As such, it lays a critical foundation for further investigations of classical conditioning
as a possible driver of persistent pain.
Perspective
This study provides new evidence that human pain thresholds can be influenced by non-nociceptive
somatosensory stimuli, via a classical conditioning effect. As such, it lays a critical
foundation for further investigations of classical conditioning as a possible driver
of persistent pain.
Key words
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Article info
Publication history
Published online: July 21, 2016
Accepted:
June 23,
2016
Received in revised form:
June 23,
2016
Received:
February 18,
2016
Footnotes
J.W.S.V. and G.L.M. contributed equally to this report as last authors.
V.J.M. was supported by the Oppenheimer Memorial Trust, South Africa, and is now supported by an Innovation Postdoctoral Scholarship from the National Research Foundation of South Africa. J.W.S.V. is supported by the Odysseus Grant, “The Psychology of Pain and Disability Research Program” funded by the Research Foundation Flanders (FWO-Vlaanderen), Belgium, as well as the “Asthenes” long-term structural funding—Methusalem grant by the Flemish Government, Belgium. G.L.M. is supported by an Australian National Health and Medical Research Council Principal Research grant (1061279). This project was supported by a project grant from the Australian National Health and Medical Research Council (1047317).
GLM has received support from Pfizer, Kaiser Permanente, Results Physiotherapy and Agile Physiotherapy. He receives speaker fees for lectures on pain and rehabilitation and royalties for books on pain and rehabilitation.
Supplementary data accompanying this article are available online at www.jpain.org and www.sciencedirect.com.
Identification
Copyright
© 2016 by the American Pain Society
