Crossing your fingers confuses your brain long enough to mess with feelings of hot, cold, and pain, a new study has found, offering a brief respite if you happen to sustain a physical injury in the area.

The study makes use of a classic pain experiment called the thermal grill illusion, which involves subjecting the index and ring fingers to heat (40°C/104°F) while applying a cold sensation (20°C/68°F) to the middle finger using special thermal pads.

In the experiment, if a person just touches the hot or cold thermal pads, they will feel only hot or cold sensations respectively. But touching them together creates the illusion of burning heat, as Hannah Devlin explains at The Guardian:

"The illusion works because the hot sensation in the outer two fingers blocks the activity in a certain cooling receptor under the skin and this "inhibition" spills out to the surrounding area of the hand. 

Activity in the cooling receptors in turn normally blocks the activity of pain receptors that are sensitive to extreme cold. As a result only mild cold is now needed to produce a painful burning sensation in the middle finger - hence the illusion."

So effectively, the simultaneous heating and cooling creates an illusion because the brain is trying to reconcile a three-way interaction between the nerve pathways that are trying to send it signals about warmth, cold and pain, all at once.

The thermal grill illusion is the perfect solution for scientists wanting to experiment with and research pain sensations in humans, because it creates the feeling without causing any lasting physical damage. 

"The thermal grill is a useful component in our scientific understanding of pain," one of the researchers, neuroscientist Angela Marotta, from the University College of London's Institute of Cognitive Neuroscience in the UK, said in a press release. "It uses a precisely-controlled stimulus to activate the brain's pain systems. This can certainly feel painful, but doesn't actually involve any tissue damage."

"Cold normally inhibits pain, so inhibiting the input from the cold stimulus produces an increase in pain signals," added one of her colleagues, Elisa Ferrè. "It's like two minuses making a plus."

Then, oddly enough, the team was able to show that by just changing the position of the affected fingers, they could greatly manipulate the pain levels experienced by their volunteers. When the volunteers were asked to cross their middle fingers over their index fingers, the burning sensation was alleviated. 

But if the experiment was adjusted and the the index finger was the one that was cooled down, with the middle and ring fingers warmed, when the volunteers crossed their middle finger over the index finger, the burning sensation actually became worse. The results have been published in Current Biology.

"Interactions like these may contribute to the astonishing variability of pain," one of the team, Patrick Haggard, said in the press release. "Our research is basic laboratory science, but it raises the interesting possibility that pain levels could be manipulated by applying additional stimuli, and by moving one part of the body relative to others."

So could people with chronic pain learn to use simple positioning and carefully applied stimuli to dull painful sensations and help them to better live through debilitating disorders? That's what the team is going to try and figure out now. In the meantime, The Guardian has got some great advice to get you through your next barefoot LEGO encounter:

"Previously, scientists have shown that swearing when you hurt yourself is not only a vocal expression of agony, but that it also reduces pain. The study, by the University of Keele, found that when people were free to let rip verbally, they could cope with mild pain for nearly 50 percent longer than those who said neutral words, such as 'table'."

Cursing is the best medicine, apparently.

Source: The Guardian