Location, location, location: Variation in sensitivity to pain across the body.

Background: There is evidence that sensitivity to noxious stimuli differs between the sexes and across the body, but few studies have investigated differences in the perception and experience of acute pain stimuli across the body in healthy individuals.
Methods: We recruited 52 healthy participants, aged 18-36 (50% men) and administered 39, 42 and 45 °C stimuli at four body sites bilaterally to examine differences in the experience of pain intensity and unpleasantness between body sites via an 11-point numerical rating scale.
Results: Noxious and innocuous thermal heat stimuli were perceived as significantly more intense when delivered to the wrist (M = 3.98, SD = 1.93) and back (M = 4.07, SD = 1.98) compared to the shoulder (M = 3.45, SD = 1.91) and leg (M = 3.46, SD = 1.87). Pain unpleasantness ratings yielded similar findings; stimuli were perceived as more unpleasant when administered to the wrist (M = 2.83, SD = 1.93) and lower back (M = 3.04, SD = 2.11) compared to the shoulder (M = 2.63, SD = 1.85) and leg (M = 2.26, SD = 1.82).
Conclusions: These findings suggest that painful thermal stimuli delivered to the wrist and back are perceived as more intense and unpleasant compared with other body sites in healthy persons. These differences may be due to variations in receptor density, or the relative importance of these sites for daily living and survival.
Significance: Moreover, these insights are helpful for the design of studies investigating pain experience in healthy persons in experimental or clinical settings. WHAT DOES THIS STUDY ADD?: We tested sensitivity to acute suprathreshold thermal stimulations across a range of body sites to investigate for potential variability. We found significant differences in the perceived intensity and unpleasantness of noxious and innocuous thermal stimuli at the wrist and lower back, compared with the shoulder and leg. These results suggest that pain experience is driven by receptor density or the relative functional importance of these sites.
(© 2016 European Pain Federation - EFIC®.)