Crossing two fingers, middle over index or ring fingers, reduced pain while uncrossing them restored pain. The spatial position of the fingers, not the part-to-body position (what the researchers call “posture”), determined weakening or strengthening of pain sensations. No real pain was inflicted, but an illusionary sensation of burning heat was stimulated through a standard laboratory test called the thermal grill illusion.
Commenting in a press release on the brain’s role in the sensations, co-author of the University College London (UCL) study, Elisa Ferrè said: “The brain seemed to use the spatial arrangement of all three stimuli to produce the burning heat sensation on just one finger.”
Thermal Grill Illusion
The thermal grill illusion — the sensation of heat or cold stimulus — is created on a special piece of equipment that stimulates sensations of heat and cold to three fingers in a grill pattern of warm-cold-warm. The warm-cold-warm grill-like pattern is known to stimulate the illusion of a burning sensation to the middle-cold finger.
As stated in Science Daily by UCL researcher Angela Marotta, the real sensation of painful burning results through stimulation of neurorecptors but without any real pain inflicted: “This can certainly feel painful, but doesn’t actually involve any tissue damage.”
It is the burning sensation, illusionary pain that was alleviated by finger crossing in the study. Researchers compared the results of a spatial alignment of warm-cold-warm to when the spatial position was changed, by crossing middle over index fingers or middle over ring fingers, to a peripheral position resulting in a cold-warm-warm pattern.
Study Results
In the thermal grill, the index is warm, the middle is cold, and the ring finger is warm. When the middle finger crosses over the index or ring fingers, the middle-cold finger takes a spatially peripheral position while the index-warm finger moves to the spatially central position. This crossing of fingers changes the grill configuration resulting in a cold-warm-warm or warm-warm-cold alignment. In this middle-finger peripheral spatial alignment configuration, the illusionary burning pain was alleviated. When the fingers were uncrossed, restoring the warm-cold-warm grill, the burning sensation was also restored.
The results showed that, surprisingly, the brain uses the spatial orientation of the finger, rather than the part-to-body position of the finger on the hand, to process incoming sensation stimulus signals from the fingers. Lead researcher, author of the study and UCL professor Patrick Haggard comments: “Interactions like these may contribute to the astonishing variability of pain.”
Interesting Correlation to He Gu Point
There is an interesting correlation of the middle-over-index pain alleviation part of the UCL pain stimulation study to the He Gu pain relief point traditionally used in acupuncture and acupressure. (Acupressure is often used for self-help while acupuncture must be performed by a licensed specialist.)
Along the outer edge of your index finger runs the extremity end of the Large Intestine (LI) Meridian used for both acupuncture and acupressure. In the soft tissue area connecting thumb to index finger lies the LI Meridian point identified as LI4 and called He Gu. This point has traditionally been used for the relief of pain.
Note that the LI Meridian, upon which LI4-He Gu lies, extends all the way up the index finger to the outer corner of the cuticle. When crossing the middle finger over the index finger, pressure is applied by the middle finger to the LI meridian. This stimulates the entire local area of the LI meridian, including the pain-relieving He Gu point between thumb and index finger.
Though not part of the study — which tracked neuroreceptor response to physical change in spatial relationships — and related only to the aspect of the study in which pain is alleviated by crossing middle over index fingers, it is intriguing to question whether meridian stimulation in the He Gu area might have an unforeseen relationship to the effectiveness of pain relief in that portion of the study.
While the thermal grill illusion tests for spatial-to-posture relevance in pain alleviation and renewal, the possibility of a correlating effect from an element of meridian-specific pressure might add another potential dimension to the application of spatial alignment for pain management.
Hypothesized Reason for Spatial Orientation Affect
Researchers and colleagues theorize that, like with optical illusions, pain receptors were stimulated by sensory illusions. The brain confuses spatial orientation for raw stimulus and, fooled by alignment in space rather than attending to part-to-body alignment, reacted to the illusion created by spatial re-alignment, or the crossing of fingers. “This is why sometimes perceptions do not accurately reflect the sensory input. Pain is a perception often only loosely related to the actual noxious sensory input,” as the sensory illusion is explained by Giandomenico Iannetti, professor and pain specialist at UCL not involved in the study. Comparing the thermal grill sensory illusion to well understood optical illusions, he further says: “Perceptions are constructed in the brain with the objective of selecting the most useful features in the world around us.” This explains what Haggard called the “astonishing variability of pain.”
Application of Research
There is a unique application of the study to the alleviation and control of chronic or severe pain. Application of the study pertains in learning how positioning can mitigate pain and how the utilization of specific, carefully applied stimuli can increase pain mitigation. Haggard comments: “Our research … raises the interesting possibility that pain levels could be manipulated 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.” Their study “Transforming the Thermal Grill Effect by Crossing the Fingers” appears online in Current Biology.
