Learning
Does classical conditioning reliably create a placebo effect for pain?
Open access · cc by · source: Europe PMC
Using a classical conditioning procedure where pill intake was paired with covertly reduced cold pain did not lead to a lasting placebo effect when the full pain stimulus returned.
Key findings
Although participants in the conditioned group rated the starch capsules as more effective compared to the capsule control group, this expectation did not transfer to actual pain relief. During the final test, where the original painful temperature returned, the conditioned group experienced no significant drop in pain unpleasantness or increase in pain threshold. Ultimately, neither the conscious belief in the pill's effectiveness nor the training sessions succeeded in producing a reliable placebo effect.
Methodology
Researchers evaluated 61 healthy participants, including 34 females and 27 males, split into three distinct experimental groups. Participants experienced cold pain applied to the forearm for 2 minutes and rated their discomfort on a scale ranging from 0 to 10. The conditioned group repeatedly took inert starch capsules paired with a secret reduction in the thermode's cold temperature, while control groups received either capsules without temperature relief or temperature changes without capsules.
Limitations
The study cannot rule out whether more training trials are necessary, as participants only experienced two conditioning rounds before the final test. Additionally, because the final post-test suddenly reintroduced the full painful temperature, this stark mismatch may have triggered surprise or anxiety, disrupting any potential placebo response. Finally, the findings are limited to acute cold pain administered via a thermode and might not generalize to other kinds of pain or clinical settings.
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