Classical Conditioning Fails to Elicit Allodynia in an Experimental Study with Healthy Humans
One page on PainSci cites Madden 2017: Chronic Pain as a Conditioned Behaviour
PainSci commentary on Madden 2017: ?This page is one of thousands in the PainScience.com bibliography. It is not a general article: it is focused on a single scientific paper, and it may provide only just enough context for the summary to make sense. Links to other papers and more general information are provided wherever possible.
This trial was a rare direct test of whether classical conditioning could induce pain from non-painful stimuli in humans, via the mechanism of classical conditioning. First, Madden et al. combined non-painful sensory stimuli (vibration) with painful heat in 34 participants. They were trying to “teach” the subjects that vibration=pain. Then they checked to see if their pain thresholds had in fact been reduced for the conditioned stimulus, by applying vibration alone.
It didn’t work: there was no statistically significant reduction in pain thresholds. On the contrary, they went up! A habituation effect, probably (see May) — the actual opposite of being conditioned to feel more pain when vibrated, these subjects were “conditioned” to feel less pain. That effect is worth understanding, regardless of the implications for conditioning of pain.
Factors like gender, lousy mood (“negative affect,” prone to fear, sadness, anxiety), and pain catastrophizing had no effect (an important detail).
The study concludes that classical conditioning definitely did not induce allodynia under these conditions, but also makes it clear “this is isn’t over,” more study really is needed:
Importantly, this study does not provide conclusive evidence that allodynia cannot be induced using classical conditioning—only that the present carefully designed paradigm did not induce allodynia in this sample. It remains possible that allodynia might be induced under different conditions—perhaps with different stimuli, different anatomical sites, or different conditions of implicit threats.
Indeed, all the key limitations of this study casting a bit more doubt on whether the conditions of the trial were fertile ground for growing a crop of conditioned pain:
- Timing! The “simultaneous” pairing of stimuli was not perfectly aligned, so maybe the conditioning wasn’t good enough.
- Vibration? Visual and auditory stimuli might have worked better (as used in other studies).
- Masking! While participants were blinded — an important feature of any trial — being unaware of the pairing might have sabotaged the conditioning a bit. (But is awareness required for classical conditioning in this context? Unknown.)
original abstract †Abstracts here may not perfectly match originals, for a variety of technical and practical reasons. Some abstacts are truncated for my purposes here, if they are particularly long-winded and unhelpful. I occasionally add clarifying notes. And I make some minor corrections.
OBJECTIVE: Associative learning has been proposed as a mechanism behind the persistence of pain after tissue healing. The simultaneous occurrence of nociceptive and non-nociceptive input during acute injury mimics the pairings thought to drive classical conditioning effects. However, empirical evidence for classically conditioned allodynia is lacking. We aimed to manipulate pain thresholds with a classical conditioning procedure that used non-nociceptive somatosensory stimuli as conditioned stimuli (CS) and nociceptive stimuli as unconditioned stimuli. We also explored the influence of gender, depression, anxiety, negative affect, and pain catastrophizing on the main manipulation.
DESIGN: Thirty-four healthy humans participated in a differential classical conditioning procedure that used vibrotactile stimulations at two different locations as CS. In an acquisition phase, CS+ was paired with painful thermal stimulation, and CS- with nonpainful thermal stimulation. Heat pain threshold was assessed during paired heat-CS trials before and after acquisition. A 2 (time: 1 and 2) x 2 (condition: CS+ and CS-) repeated-measures analysis of variance compared pain thresholds before and after acquisition. Exploratory analyses explored the influence of gender, depression, anxiety, negative affect, and pain catastrophizing. Postexperiment questions investigated participants' awareness of the contingencies employed.
RESULTS: The classical conditioning procedure did not alter pain thresholds. Exploratory analyses did not reveal any influence of individual differences. Thirty of the 34 participants were unaware of the contingencies between stimuli.
CONCLUSIONS: The results of this study provide no evidence that allodynia can be induced in healthy humans using a classical conditioning procedure with simultaneous timing.
related content
- “Within-session sensitization and between-session habituation: a robust physiological response to repetitive painful heat stimulation,” May et al, European Journal of Pain, 2012.
This page is part of the PainScience BIBLIOGRAPHY, which contains plain language summaries of thousands of scientific papers & others sources. It’s like a highly specialized blog. A few highlights:
- Classical Conditioning Fails to Elicit Allodynia in an Experimental Study with Healthy Humans. Madden 2017 Pain Med.
- Topical glyceryl trinitrate (GTN) and eccentric exercises in the treatment of mid-portion achilles tendinopathy (the NEAT trial): a randomised double-blind placebo-controlled trial. Kirwan 2024 Br J Sports Med.
- Placebo analgesia in physical and psychological interventions: Systematic review and meta-analysis of three-armed trials. Hohenschurz-Schmidt 2024 Eur J Pain.
- Recovery trajectories in common musculoskeletal complaints by diagnosis contra prognostic phenotypes. Aasdahl 2021 BMC Musculoskelet Disord.
- Cannabidiol (CBD) products for pain: ineffective, expensive, and with potential harms. Moore 2023 J Pain.