Pavlovian dogs – these were the dogs in whose presence a bell was rung at every meal. After a short time the ringing of the bell sufficed to stimulate the flow of saliva in the animals – they had been conditioned, and in 1904 their eager experiment-loving master was even awarded the Nobel Prize for these experiments. A similar conditioning process could also help people with chronic pain, as scientists were able to demonstrate in an experiment recently published in the journal PLOS One.
The pain-displaces-pain principle
It has long been known that a new pain can virtually displace an existing one. So, when you ram a toe into the door, this ends up hurting less if you follow up with a hammer blow to your thumb. During this process the human nerve system blocks the first pain so that more attention is able to be given to the second, possibly more relevant one. Scientists now have combined this “pain-represses-pain” principle with the Pavlovian effect – but using a trick, since generating a new pain naturally brings little relief to pain patients by only having the body distracted away from the old one.
Electric surges in the foot
32 subjects participated in an experiment done by scientists from Luxembourg and the United States. In order to produce a first pain, the subjects received light but painful electric shocks to the foot. The intensity of pain was recorded by scientists by having the subjects evaluate the perceived pain on a scale from 1 to 10, and measuring the effects of pain sensation such as in muscle twitching.
Hand into ice water
The researchers used ice water as a second pain stimulus, into which the subjects were asked to immerse one hand after the electric discharge in the foot. As expected, the pain impulse in the foot yielded. Here the Pavlovian effect comes into play: a number of the experiment participants heard through headphones while dipping a hand into the bucket of ice water the ringing of a telephone.
After six runs, for these subjects it was already enough for the phone to ring in order to relieve the pain in the foot. Compared to the control group not exposed to the ringtone, the pain sensation for these subjects was not only subjectively weaker, but also objectively, the physical signs of pain, such as wincing or grimacing, were markedly reduced.
Findings for pain management
“We have shown that, just as with the physiological reaction in Pavlovian dogs, such an effect and ability exist when working with humans in order to blank out pains”, says Fernand Anton, Professor of Biological Psychology at the University of Luxembourg.”Conversely, similar learning effects possibly play a role in increasing and maintaining pain in some patients”, adds Raymonde Scheuren, researcher responsible for this study. That would mean that people can also train themselves to feel pain more strongly in association with certain signals. Both findings could play an important role in pain management. Moreover, researchers first have to clarify how long such pain conditioning persists in humans. The researchers led by Anton are now working on this.