Is there a relationship between throbbing pain and arterial pulsations?

Pain can have a throbbing quality, especially when it is severe and disabling. It is widely held that this throbbing quality is a primary sensation of one's own arterial pulsations, arising directly from the activation of localized pain-sensory neurons by closely apposed blood vessels. We examined this presumption more closely by simultaneously recording the subjective report of the throbbing rhythm and the arterial pulse in human subjects of either sex with throbbing dental pain-a prevalent condition whose pulsatile quality is widely regarded a primary sensation. Contrary to the generally accepted view, which would predict a direct correspondence between the two, we found that the throbbing rate (44 bpm ± 3 SEM) was much slower than the arterial pulsation rate (73 bpm ± 2 SEM, p < 0.001), and that the two rhythms exhibited no underlying synchrony. Moreover, the beat-to-beat variation in arterial and throbbing events observed distinct fractal properties, indicating that the physiological mechanisms underlying these rhythmic events are distinct. Confirmation of the generality of this observation in other pain conditions would support an alternative hypothesis that the throbbing quality is not a primary sensation but rather an emergent property, or perception, whose "pacemaker" lies within the CNS. Future studies leading to an improved understanding of the neurobiological basis of clinically relevant pain qualities, such as throbbing, will also enhance our ability to measure and therapeutically target severe and disabling pain.