A new UCL study defines for the first time how our ability to identify where it hurts, called 'spatial acuity,' varies across the body, being most sensitive at the forehead and fingertips
"Where does it hurt?" is the first question asked to any person in pain.
Researchers from University College London use lasers to stimulate pain in a volunteer's hand. Sometimes only one laser would be activated, and sometimes both would be, unknown to participants. They were asked whether they felt one 'sting' or two, at varying distances between the two beams. The researchers recorded the minimum distance between the beams at which people were able to accurately say whether it was one sting or two. The ability to accurately discriminate the source of pain is known as 'spatial acuity' for pain.
Credit: UCL (University College London)
A new UCL study defines for the first time how our ability to identify where it hurts, called "spatial acuity", varies across the body, being most sensitive at the forehead and fingertips.
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. The work is published in the journal Annals of Neurology and was funded by the Wellcome Trust.
With the exception of the hairless skin on the hands, spatial acuity improves towards the centre 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."
Volunteers were blindfolded and had specially-calibrated pairs of lasers targeted at various parts of their body. These lasers cause a brief sensation of pinprick pain. Sometimes only one laser would be activated, and sometimes both would be, unknown to participants. They were asked whether they felt one 'sting' or two, at varying distances between the two beams. The researchers recorded the minimum distance between the beams at which people were able to accurately say whether it was one sting or two.
"This measure tells us how precisely people can locate the source of pain on different parts of their body," explains senior author Dr Giandomenico Iannetti of the UCL Department of Neuroscience, Physiology and Pharmacology.
"Touch and pain are mediated by different sensory systems. While tactile acuity has been well studied, pain acuity has been largely ignored, beyond the common textbook assertion that pain has lower acuity than touch. We found the opposite: acuity for touch and pain are actually very similar. The main difference is in their gradients across the body. For example, pain acuity across the arm is much higher at the shoulder than at the wrist, whereas the opposite is true for touch."
Acuity for both touch and pain normally correlates with the density of the relevant nerve fibres in each part of the body. However, the fingertips remain highly sensitive despite having a low density of pain-sensing nerve cells.
"The high pain acuity of the fingertips is something of a mystery that requires further investigation," says Dr Mancini. "This may be because people regularly use their fingertips, and so the central nervous system may learn to process the information accurately."
The findings have important implications for the assessment of both acute and chronic pain. Dr Roman Cregg of the UCL Centre for Anaesthesia, who was not involved in the research, is a clinical expert who treats patients with chronic pain.
"Chronic pain affects around 10 million people 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 Cregg. "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."
Harry Dayantis | Eurek Alert!
Climate study finds evidence of global shift in the 1980s
26.11.2015 | Leibniz-Institut für Gewässerökologie und Binnenfischerei (IGB)
Network analysis shows systemic risk in mineral markets
16.11.2015 | International Institute for Applied Systems Analysis (IIASA)
Before the fluid of the middle ear drains and sound waves penetrate for the first time, the inner ear cells of newborn rodents practice for their big debut. Researchers at Johns Hopkins report they have figured out the molecular chain of events that enables the cells to make “sounds” on their own, essentially “practicing” their ability to process sounds in the world around them.
The researchers, who describe their experiments in the Dec. 3 edition of the journal Cell, show how hair cells in the inner ear can be activated in the absence...
Planet Earth experienced a global climate shift in the late 1980s on an unprecedented scale, fuelled by anthropogenic warming and a volcanic eruption, according to new research published this week.
Scientists say that a major step change, or ‘regime shift’, in the Earth’s biophysical systems, from the upper atmosphere to the depths of the ocean and from...
The Fraunhofer Institute for Solar Energy Systems ISE has installed 70 photovoltaic modules on the outer façade of one of its lab buildings. The modules were...
Nerve cells cover their high energy demand with glucose and lactate. Scientists of the University of Zurich now provide new support for this. They show for the first time in the intact mouse brain evidence for an exchange of lactate between different brain cells. With this study they were able to confirm a 20-year old hypothesis.
In comparison to other organs, the human brain has the highest energy requirements. The supply of energy for nerve cells and the particular role of lactic acid...
In laser material processing, the simulation of processes has made great strides over the past few years. Today, the software can predict relatively well what will happen on the workpiece. Unfortunately, it is also highly complex and requires a lot of computing time. Thanks to clever simplification, experts from Fraunhofer ILT are now able to offer the first-ever simulation software that calculates processes in real time and also runs on tablet computers and smartphones. The fast software enables users to do without expensive experiments and to find optimum process parameters even more effectively.
Before now, the reliable simulation of laser processes was a job for experts. Armed with sophisticated software packages and after many hours on computer...
30.11.2015 | Event News
25.11.2015 | Event News
17.11.2015 | Event News
30.11.2015 | Trade Fair News
30.11.2015 | Trade Fair News
30.11.2015 | Trade Fair News