Pain radiation depends on skin type, intensity and duration of noxious exposure

Background & Aims

Many chronic pain conditions are characterized by widespread, non-dermatomal pain distribution with radiation. However, the mechanisms behind pain radiation remain elusive. In this study, we present the results of a psychophysical investigation. We hypothesized that more intense noxious stimuli would lead to larger areas of perceived pain that reflect pain radiation, while more intense light would not produce radiation. We also investigated how skin type (glabrous vs. hairy) and stimulus duration influence pain radiation patterns.

Methods

Four temperature stimuli (43°C, 45°C, 47°C, and 49°C) were applied to both glabrous (hand) and hairy (forearm) skin for 5 seconds and 10 seconds. Visual stimuli of varying intensities were also presented on these areas. Fifty healthy participants (age: 24.98 ? 7.54 years, 26 females) provided ratings for both pain and light intensity, as well as pain and light extent. In the extent rating, participants matched the displayed square’s size to their experienced pain or light extent.

Results

The following observations were found in this experiment: i) pain radiated extensively as indicated by 13.4? greater area of pain perceived compared to the actual area of the stimulation with 49°C (p < 0.001), which was not the case in the visual extent ratings (1.2?), ii) pain radiation was greater in hairy compared to glabrous skin (p < 0.05) and with longer compared to shorter stimulus duration (p < 0.001), iii) accuracy of extent ratings were exceptionally high: visual percept was not different from the size of visual stimuli displayed, iv) individual differences in perceived pain intensity explained only 14% of individual differences in radiation.

Conclusions

These data indicate that the spatial tuning mechanisms of the nociceptive system are substantially different from those of the visual system. Thus, the efficient lateral inhibition processes present in vision that prevent perceptual expansion are not present in the nociceptive system, which may rely on more distributed and complex patterns of neuronal recruitment at the spinal cord level and population coding mechanisms in the nervous system.

References

[1] Coghill R. C. (2020). The Distributed Nociceptive System: A Framework for Understanding Pain. Trends in neurosciences, 43(10), 780–794.
[2] Naugle, K. M., Cruz-Almeida, Y., Fillingim, R. B., Staud, R., & Riley, J. L., 3rd (2017). Increased spatial dimensions of repetitive heat and cold stimuli in older women. Pain, 158(5), 973–979.
[3] Price, D. D., Hayes, R. L., Ruda, M., & Dubner, R. (1978). Spatial and temporal transformations of input to spinothalamic tract neurons and their relation to somatic sensations. Journal of neurophysiology, 41(4), 933–947.

Presenting Author

Waclaw M. Adamczyk

Poster Authors

Waclaw Adamczyk

PhD

Akademia Wychowania Fizycznego w Katowicach

Lead Author

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