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Comparison of spatial summation properties at different body sites

PainSci » bibliography » Holbert et al 2017
Tags: chronic pain, neat, pain problems

Three articles on PainSci cite Holbert 2017: 1. The Complete Guide to Trigger Points & Myofascial Pain2. The Complete Guide to Neck Pain & Cricks3. 38 Surprising Causes of Pain

PainSci notes on Holbert 2017:

Pain is more intense if the causes are more spread out (“spatial summation”), which may explain why some areas of the body are more prone to pain — because there’s simply a greater chance of more sources of pain. Specifically, it may explain why spinal pain is so prevalent: many potential sources of nociception in a region. This data shows that summation in the neck and back works about the same way that it does in the limbs. In any region, painful sites separated by as much as 15-20cm will be “summed” by the brain, making the entire area feel painful. So spinal pain is not more common because of casting a wider summation net. However, there may still be more to sum.

original abstract Abstracts here may not perfectly match originals, for a variety of technical and practical reasons. Some abstacts are truncated for my purposes here, if they are particularly long-winded and unhelpful. I occasionally add clarifying notes. And I make some minor corrections.

BACKGROUND AND AIMS: The nociceptive system appears to have evolved a range of protective characteristics that are of great interest in understanding both acute and chronic pain. Spatial summation is one important characteristic, whereby increasing area of a stimulus, or distance between multiple stimuli, results in more intense pain-not only greater area of pain. One of the mysteries of chronic pain is why spinal pain is so prevalent relative to pain at other sites. Since pathological tissue models have failed to fully explain spinal pain, we theorized that body region specific differences in sensory processing-such as a greater propensity for spatial summation-may help to explain its vulnerability. We aimed to examine this by comparing the properties of summation at different body parts: the dorsal forearm, neck, and back.

METHODS: Spatial summation of pain was investigated using noxious intra-dermal electrical stimuli in healthy pain-free adults (14 males, 6 females), and the perceived pain intensity was rated on a 0-100 pain scale. Area-based stimulation was investigated by doubling the stimulation area with the addition of a second electrode placed adjacent to the first. Distance-based summation was investigated by randomly varying the separation distance between paired noxious electrical stimuli at separations of 0, 10, 15, and 20cm.

RESULTS: This study demonstrated that the properties of area- and distance-based summation are uniform across the neck, back, and forearm in healthy adults. Spatial summation of pain was also found to be greatest at 15- and 20-cm paired separations for all body regions tested, confirming that noxious information can be integrated over an extensive anatomical area.

CONCLUSION: Data from this investigation refutes the thesis that spatial summation of pain may be a contributing factor for the reported difference in chronicity rates between spinal and peripheral sites. It remains, however, a potentially important mechanism by which noxious inputs from multi-level pathology might integrate and contribute to pain.

IMPLICATIONS: While data from this project suggest that there are no regional differences in the properties of spatial summation of noxious stimuli, regional differences in other characteristics of the nociceptive system may yet provide insight into why some spinal pain is so highly prevalent; nociceptive distance-based summation may be highly relevant where two or more conditions co-exist in close proximity.

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