ABSTRACT
In the late nineteenth century, physiologists began to regard pain as a sensation. At first this seemed to be a strange idea, because pain is so closely associated with suffering and hence with the realm of emotions. One of the first scientists relating pain to certain mechanisms of transmission of peripheral stimuli into the central nervous system was René Descartes in the seventeenth century. He outlined his idea of nerve conduction on the example of heat pain, thus placing it alongside the classical sense of vision (Descartes 1969). In the early nineteenth century, at the dawn of a naturalistic physiology, Johannes Mueller formulated his “Gesetz der spezifischen Sinnesenergien,” i.e., the postulate that each sense is subserved by its specific neuronal sensory and nervous apparatus (Mueller 1837). In the last decade of the nineteenth century, when physiology had reached a first peak as a natural science, several researchers made the observation that the skin, our largest sensory organ, can be regarded as a mosaic of sensory spots that can be stimulated separately with fine probes to evoke pure sensations of touch, warmth, or cold. Pioneers of this research were the Swedish physiologist Blix, the German Goldscheider, and the Austrian/ German von Frey. Max von Frey was the most systematic and important of this group. He developed an easy and reliable method to stimulate the “touch points” with “Tasthaar” stimulators, nowadays called “von Frey filaments.” By employing thin and sharp plant spicules he found locations between the touch points where such a fine spicule could induce pain without accompanying touch sensation. From this finding he deduced his famous “specificity theory” of pain. One can still have a feeling of his enthusiasm for this discovery when he wrote (von Frey 1896; see also Handwerker and Brune 1987, p. 95)
“It is possible to stimulate the skin in such a way as to produce a painful sensation with no preceeding or accompanying pressure sensation. That this can be done … leads to the conclusion that pain is the result of exciting special organs … the pain points are a sign of the irregular distribution of specifically pain sensitive organs over the skin.”
