If you've ever hurt yourself - bumped a leg or arm while walking, maybe - you might have instinctively grabbed the place that hurt, and that seemed to ease the pain. Now, new research on pain and self touch explores why that is.
To study the phenomenon, European researchers used a variation of what's known as the thermal grill illusion. It's a quirk of sensation that if you warm your second and fourth fingers and chill the middle finger, that cold finger will paradoxically feel hot, painfully hot.
That's useful for scientific experiments because the pain is real, but isn't caused by any actual harm.
In this study, people in the experiment put both hands through the thermal grill illusion, then touched the three middle fingers on the two hands together. That produced a big reduction in the sensation of painful heat, which earlier studies predicted.
But researcher Marjolein Kammers of University College London says the pain reduction came only when they touched their own fingers. When they were touched by another person who had also gone through the thermal grill experience, their finger felt just as hot.
"And this was interesting," she said, "because in terms of low-level feedback to the brain, you get similar touch and thermal feedback. "The only difference is, is that it's not self-touch. And that made us realize that it's about integrating both hands into a more coherent representation of the body."
Kammers says pain can result from confusion in what she describes as the brain's representation of the body. She illustrates the concept with the often severe pain amputees report feeling in their missing limb.
"The best example of what can happen when the body representation is disturbed is phantom limb pain, where one hypothesis is that the brain needs to be updated with a representation of the body. So the body has lost a limb, but the brain still represents it as being present. And this mismatch can cause pain."
In an interview via Skype, Kammers says if she and her colleagues get a better understanding of the power of self-touch to ease pain, it might become part of pain treatment.
"That's the ultimate goal. That would be great if that would be possible."
And Kammers says she does think that may be possible. Her study on the effect of touch, specifically self-touch, on pain, is published in Current Biology.