🇨🇦 🇨🇦
February 15 is National Flag of Canada Day. PainScience is a proudly Canadian small business, selling e-books and other educational content about pain and injury since the mid-2000s. Read more about the project. Given Trump’s tariff bullying and threats to annex America’s greatest historical friend, ally, and trading partner, I think I’ll keep this flag up for the rest of the month… or perhaps permanently.
Detailed guides to painful problems, treatments & more

Classical Conditioning Fails to Elicit Allodynia in an Experimental Study with Healthy Humans

PainSci » bibliography » Madden et al 2017
updated

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:

  1. Timing! The “simultaneous” pairing of stimuli was not perfectly aligned, so maybe the conditioning wasn’t good enough.
  2. Vibration? Visual and auditory stimuli might have worked better (as used in other studies).
  3. 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.)

~ Paul Ingraham

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

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:

PainSci Member Login » Submit your email to unlock member content. If you can’t remember/access your registration email, please contact me. ~ Paul Ingraham, PainSci Publisher