When touch predicts pain: predictive tactile cues modulate perceived intensity of painful stimulation independent of expectancy

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Harvie, Daniel S
Meulders, Ann
Madden, Victoria J
Hillier, Susan L
Peto, Daniela K
Brinkworth, Russell
Moseley, G Lorimer
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2016
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Abstract

Aims: Non-nociceptive somatosensory input, such as tactile or proprioceptive information, always precedes nociceptive input during a painful event. This relationship provides clear opportunities for predictive associative learning, which may shape future painful experiences. In this differential classical conditioning study we tested whether pain-associated tactile cues (conditioned stimuli; CS) could alter the perceived intensity of painful stimulation, and whether this depends on duration of the CS—seeing that CS duration might allow or prevent conscious expectation. Methods: Subjects underwent a classical differential conditioning task in which a tactile cue at location A (CS+) preceded painful electrical stimulation at location B (UShigh), whereas a tactile cue at location C (CS−) preceded non-painful electrical stimulation at location B (USlow). At test, we compared the pain evoked by a moderately painful stimulus (USmed) when preceded by either the CS+ or CS−. CS duration was manipulated between subjects. Participants were assigned to one of three groups: Long CS (4 s, allowing conscious expectation), Short CS (110 ms) and CS-US indistinguishable (20 ms), preventing conscious expectation). We hypothesised that more pain would be evoked by the US when preceded by the CS+ relative to the CS-, and that the effect would be independent of CS duration. Results: Fifty-four healthy participants (31 females, age = 26, SD = 9) were included in the analysis. The hypotheses were supported in that more intense pain was evoked by the USmed when paired with the tactile CS+, than when paired with the tactile CS-; mean difference 3 mm on a 150 mm VAS (CI 0.4–4.8 mm). CS duration did not moderate the effect. The effect was greater in those participants where calibration was optimal, as indicated by a relatively more painful UShigh. Conclusion: We conclude that pain-associated tactile cues can influence pain, and that this effect is not dependent on stimulus duration. This suggests that explicit expectation is not a requirement for predictive cues to modulate pain. That the presence of the CS+ resulted in only a 5.3% higher intensity rating compared with the CS− may reflect a limitation of laboratory studies, where a limited number of trials, an artificial context and the use of experimental pain are likely to reveal only glimpses of what is clinically possible.

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Scandinavian Journal of Pain

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11

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1

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Clinical sciences

Clinical sciences not elsewhere classified

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