Researchers used a variant of a popular pain experiment known as the “thermal grill illusion”, where a pattern of warm-col-warm temperatures are applied to the index, middle and ring finger respectively results in a somehow strange sensation of burning heat in the middle finger – the one that received the cold stimulus.
Co-lead author in the research, Angela Marotta from UCL Institute of Cognitive Neuroscience, says “The thermal grill is a useful component in our scientific understanding of pain. 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 experiments results ina burning hear sensation because the nerve pathways have a three-way interaction, telling the brain about the warmth, cold, and pain. The warm temperatures on the index and ring fingers blocks the brain activity that otherwise would result from the cold temperature on the middle finger.
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.
The researchers were funded by the European Union Seventh Framework Programme (EU FP7) project VERE.
The findings were published in Current Biology.