A new study from the University College London has defined for the first time how a person’s ability to recognize where it hurts, called “spatial acuity,” differs across the body. The study found the most sensitive areas are on the forehead and fingertips.

These findings have important significance for the assessment of acute and chronic pain, according to an article in Science Daily. The following is an excerpt from the article….

Using lasers to cause pain to 26 healthy volunteers without any touch, the researchers produced the first systematic map of how acuity for pain is distributed across the body.

With the exception of the hairless skin on the hands, spatial acuity improves towards the center of the body whereas the acuity for touch is best at the extremities. This spatial pattern was highly consistent across all participants.

The experiment was also conducted on a rare patient lacking a sense of touch, but who normally feels pain. The results for this patient were consistent with those for healthy volunteers, proving that acuity for pain does not require a functioning sense of touch.

“Acuity for touch has been known for more than a century, and tested daily in neurology to assess the state of sensory nerves on the body. It is striking that until now nobody had done the same for pain,” says lead author Dr. Flavia Mancini of the UCL Institute of Cognitive Neuroscience. “If you try to test pain with a physical object like a needle, you are also stimulating touch. This clouds the results, like taking an eye test wearing sunglasses. Using a specially-calibrated laser, we stimulate only the pain nerves in the upper layer of skin and not the deeper cells that sense touch.”

“Chronic pain affects around 10 million in the UK each year according to the British Pain Society, but we still have no reliable, reproducible way to test patients’ pain acuity,” says Dr. Roman Cregg of the UCL Centre for Anaesthesia. “This method offers an exciting, non-invasive way to test the state of pain networks across the body. Chronic pain is often caused by damaged nerves, but this is incredibly difficult to monitor and to treat. The laser method may enable us to monitor nerve damage across the body, offering a quantitative way to see if a condition is getting better or worse. I am excited at the prospect of taking this into the clinic, and now hope to work with Drs. Mancini and Iannetti to translate their study to the chronic pain setting.     Science Daily   6/6/14

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