Does classical conditioning reliably create a placebo effect for pain?
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.
Source
Failure to Find a Conditioned Placebo Analgesic Response
What they did
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.
What they found
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.
The limits
What it doesn't show
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.
Key terms
- Placebo analgesia
- A reduction in pain that occurs after receiving an inactive treatment combined with the belief or suggestion that the treatment will relieve pain.
- Classical conditioning
- A learning process where a neutral stimulus becomes associated with a meaningful stimulus, eventually triggering a similar response on its own.
- Thermode
- A temperature-controlled stimulator device used in research to apply precise heat or cold to a participant's skin.
- Numerical rating scale (NRS)
- A subjective measurement tool where individuals verbally rate their pain, stress, or other sensations on a designated numerical spectrum.
- Nocebo response
- A phenomenon where an inactive substance or suggestion leads to worsening symptoms or increased sensitivity to pain.
- Cortisol
- A physiological hormone frequently measured in saliva or blood to index an individual's biological stress response.
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Quiz yourself
What sex-based hypothesis regarding the conditioned placebo response did this study specifically investigate?
Common questions
Why did the researchers secretively lower the temperature during the conditioning phase?
They lowered the temperature to trick participants into thinking the placebo capsule was actively reducing their pain, thereby training their brains to associate taking the capsule with relief.
Did the sex of the experimenter play any role in how participants rated the placebo?
Yes, participants rated the capsules as more effective when they were administered by a male experimenter, though the reasons remain unclear since the male and female experimenters had different educational backgrounds.
How does this study's failure to find a placebo effect compare to other research?
While many classical conditioning studies successfully produce placebo effects, some recent research similarly shows that conditioning alone—without explicit verbal suggestions of pain relief—fails to generate a reliable placebo response.
Could previous experience with painkillers have influenced the results?
It is highly likely; even the control group that received the capsules without any temperature reduction rated them as somewhat effective, suggesting their prior real-life history with medicine created automatic expectations of relief.
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