London: How you feel pain is affected by where sources of pain are in relation to
each other, and so crossing your fingers can change what you feel on a single
finger, finds new UCL research. The research, published in Current Biology, used a variation on an
established pain experiment, known as the “thermal grill illusion”. In the
thermal grill illusion, a pattern of warm-cold-warm temperatures applied to the
index, middle and ring finger respectively causes a paradoxical, sometimes
painful, sensation of burning heat on the middle finger – even though this
finger is actually presented with a cold stimulus.
“The thermal grill is a useful component in our scientific understanding
of pain,” says Angela Marotta (UCL Institute of Cognitive Neuroscience),
co-lead author in the research, “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.”
The thermal grill produces burning heat sensations because of a three-way
interaction between the nerve pathways that tell the brain about warmth, cold
and pain. The warm temperature on the ring and index fingers blocks the brain
activity that would normally be driven by the cold temperature on the middle
finger.
"Cold normally inhibits pain, so inhibiting the input from the cold
stimulus produces an increase in pain signals,” explains co-lead author Dr
Elisa Ferrè (UCL Institute of Cognitive Neuroscience). “It’s like two minuses
making a plus.”
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.
Professor Patrick Haggard
The researchers showed that this interaction was based on the spatial
arrangement of the fingers. When the middle finger was crossed over the index
finger, the paradoxical sensation of burning heat on the middle finger was
reduced.However, if the index finger was cooled and the middle and ring fingers
were warmed, the burning heat sensation was now increased when the middle
finger was crossed over the index finger.
“Our results showed that a simple spatial pattern determined the burning
heat sensation,” says Dr Ferrè. “When the cold finger was positioned in between
the two warm fingers, it felt burningly hot. When the cold finger was moved to
an outside position, the burning sensation was reduced. The brain seemed to use
the spatial arrangement of all three stimuli to produce the burning heat
sensation on just one finger.”
“Interactions like these may contribute to the astonishing variability of
pain,” says senior author Professor Patrick Haggard (UCL Institute of Cognitive
Neuroscience). “Many people suffer from chronic pain, and the level of pain
experienced can be higher than would be expected from actual tissue damage. 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. Changing the spatial pattern of
interacting inputs could have an effect on the brain pathways that underlie
pain perception.”
The researchers were funded by the European Union Seventh Framework
Programme (EU FP7) project VERE, Work Package 1.
- See more at: http://www.ucl.ac.uk/news/news-articles/0315/260315-Crossing-fingers-reduce-pain#sthash.J0ynNpkB.dpuf