Prehistoric people had no difficulty in understanding pain associated with injury, but they were mystified by pain caused by disease. Such pain was linked with intrusion of certain objects or evil spirits into the body and treatment consisted of extracting the intruding object, fighting away the demon, or supplicating the gods. Ancient Egyptians and Babylonians believed that pain from disease was caused by influences of gods or the spirit of the dead, and was perceived in the heart and blood vessels and not in the brain. In India, Buddhist and Hindu thought in general recognized pain as a sensation, but gave greater significance to its emotional aspects and, like the Egyptians and some ancient Greeks, believed it was experienced in the heart. In the Nei Ching, the Chinese Canon of Medicine which traces back to the time of Huang Ti, the yellow Emperor (2,600 B.C.), and published a couple hundred years before Christ, pain and disease were considered to be caused by excesses or deficits of body fluids and imbalance of Yin and Yang, which could be corrected with acupuncture.
The ancient Greeks were intensely interested in the nature of sensory data, and the sense organs of the body found a prominent place in their physiologic speculations. Pythagoras (566-497 B.C.), the first Greek thinker, who traveled widely to Egypt, Babylon, and India, apparently stimulated his disciple Alemaeon to carry out intensive study of the senses. Alemaeon, without apparent precedent, produced the idea that the brain, not the heart, was the center for sensation and reason. Despite the support by Democritus, Anaxagoras, and Plato, this view did not gain widespread acceptance, due in part to the opposition of Empedocles and above all, Aristotle, for whom the heart constituted the “sensorium commune.” Anaxogoras (500-428 B.C.) saw sensation as a quantitative change in the subject, resulting from the contrast of opposites. All sensations, he held, must be associated with pain and the more the subject and the object are unlike or contrary, the more intense is the sensation of pain. He believed that all sensations, indeed, all life, contained its element of pain, locating the perception of the sensitivity in the brain. Plato (427-347 B.C.) believed that sensation in man resulted from the movement of atoms communicating through veins to the soul. He believed that pain could arise not only from peripheral stimulation but as an emotional experience in the soul. Hippocrate’s son-in-law, Polypus, in his book The Nature of Man, wrote “pain is felt when one of the humoral elements is in deficit or excess,” thus suggesting a conceptualization similar to that held by contemporary Chinese physicians, as previously mentioned.
Aristotle (384-322 B.C.) considered touch as one of the five senses and believed that pain resulted when an excess of vital heat caused an increase in the sensitivity of touch, which arose from the flesh and was conveyed by the blood to the heart where pain was experienced. Like most other Greek philosophers, Aristotle believed that the pain experience was a negative emotion, a “quale,” or quality of the soul and a state of feeling opposite to pleasure and the epitome of unpleasantness.
Soon after Aristotle’s death, Stratton reintroduced the concept that the sensation of pain was perceived in the brain, and Herophilus (335-280 B.C.) and Erasistratus (310-250 B.C.) of Alexandria provided anatomic evidence that the brain was part of the nervous system and the nerves attached to the neuraxis were of two kinds: those for movements and those for feeling. For nearly four centuries this work was lost to the Roman world until rescued by Galen (130-201 A.D.) who acquired a massive amount of knowledge about the central and peripheral nervous systems and nerve supply of the viscera. He classified nerves as “soft,” to which he attributed sensory functions, as “hard,” which were motor nerves, and a third type concerned with nociceptive (pain) sensation. His anatomic studies prompted him to suggest a neural basis for paralysis, sensory dysfunctions, and pain due to disease and injury.
As the ignorance and superstition of the Dark Ages settled over Europe after the fall of Rome, the works of Galen, Herophilus, and Erasistratus virtually disappeared, but Aristotle’s physiology survived. During this period, the center of medicine shifted to Arabia, where Avicenna (980-1038 A.D.) codified all available medical knowledge, including the etiology and mechanism of 15 different varieties of pain. Avicenna appears to be the first to suggest that pain was a separate and distinct sense.
The Renaissance fostered a great scientific spirit to encourage many remarkable advances in chemistry, physics, physiology, and anatomy, but especially of the nervous system by such outstanding men as Mondini, Eustachius, da Vinci, Vesalius, Varolio, and others, all of whom considered pain as a sensory event carried by the nerves of touch and experienced in the brain. Despite evidence to the contrary, the Aristotelian concept of pain as a passion of the soul felt in the heart and a doctrine of the five senses prevailed for 23 centuries. Thus, William Harvey, who in 1628 discovered the circulation, still believed that the heart was the site where pain was felt.
In contrast, Descartes (1596-1650 A.D.), Harvey’s contemporary, adhered to Galenic physiology and considered the brain the seat of sensation and motor function. In his book, L’Homme (Man) published in 1664 (14 years after his death), Descartes described the conduction of sensation including pain via “delicate threads” contained in nerves which connected the tissues to the brain. Peripheral stimulation by burning, for example, caused minute particles of fire to pull upon the delicate cord just like pulling at the end of a rope to strike a bell. This was the precursor of the specificity theory which was introduced two centuries later.
During the 17th and 18th centuries, great progress was made in knowledge of the anatomy and physiology of various parts of the central nervous system by Willis, Borelli, Baglivi, Malpighi, von Haller, and others. Moreover, the anatomy and some of the physiology of the sympathetic nervous system were defined by Winslow and others. During the last part of this period (1794), Erasmus Darwin, grandfather of Charles Darwin, regarded pain as a phase of unpleasantness and said that pain resulted “whenever the sensorial motions are stronger than usual. . . A great excess of light. . . of pressure or distention. . . of heat. . . of cold produces pain.” He thus anticipated the intensive theory of pain that was introduced several decades later.
The scientific study of sensation in general and pain in particular in the modern sense really began in the first half of the 19th century when physiology emerged as an experimental science. This era was initiated in part by the publications of Bell and Magendie who demonstrated with animal experiments that the function of the dorsal roots of spinal nerves is sensory, and that of the ventral roots is motor. The impetus to the scientific study of pain was further enhanced by the writings of Weber and of Muller. In contrast to the older concepts, Weber, in his writings of 1846, distinguished between touch and pain by classifying touch as the sense of the skin and pain as belonging to “Gemeingefuhl,” an expression denoting common sensibility possessed by the skin and the internal organs. At about the same time, Muller presented “The Doctrine of Specific Nerve Energies,” which stated that the brain received information about external objects and body structures only by way of the sensory nerves, and the sensory nerves for each of the five senses carried a particular form of energy specific for each sensation. Mueller’s concept, then, was that of a straight-through system from the sensory organ to the brain center responsible for the sensation. During the ensuing half century anatomic, physiologic, and histologic studies were done that prompted the formulation of two physiologic theories of pain, the specificity theory and the intensive theory.
The specificity (or sensory) theory stated that pain was specific sensation with its own sensory apparatus independent of touch and other senses. This theory, which, as previously mentioned, had been first suggested by Avicenna and later by Descartes and also by Lotze in 1853 was definitely formulated by Schiff in 1858 following analgesic experiments in animals. Noting the effects of various incisions in the spinal cord, he found that pain and touch were independent; Section of the grey matter of the spinal cord eliminated pain but not touch, and a cut through the white matter caused touch to be lost, but pain was unaffected. The results of these vivisections were promptly corroborated by clinical evidence as a number of clinicians reported pathologic cases of disease or injured spinal cords with similar sensory defects. The theory was reaffirmed by the evidence examined by Funke in 1879 and by the classical experiments of Blix in 1882 and Goldscheider and Donaldson in 1884 who discovered separate spots for warmth, cold, and touch in the skin. A decade later von Fret extended these studies to map out pain and touch spots, but he also did histologic examination of skin intended to identify specific end-organs responsible for each sensation. On the basis of his findings and some imaginative deductions, von Frey expanded Muller’s concept of the sense of touch to four major cutaneous modalities: touch, warmth, cold, and pain. von Frey’s theory, which dealt only with receptors, prompted others to believe that pain is subserved by specific fibers from the receptors to spinal cord and specific pain pathways in the neuraxis. Experiments were carried out in peripheral nerves to show there is a one-to-one relationship between receptor type, fiber size, and quality of experience. Other animal experiments suggested that the anterolateral quadrant of the spinal cord was critically important for pain sensation, a concept which was reinforced by Spiller’s observation of analgesia with pathologic lesions of this part of the cord and the early results with anterolateral cordotomy by Spiller and Martin and many others.
The intensive theory, which was first anticipated by Darwin and subsequently suggested by Romberg, Henle, Volkmann, and Weber in the 1840s, was explicitly formulated by Erb in 1874, who maintained that every sensory stimulus was capable of producing pain if it reached sufficient intensity. This theory received subsequent support from Wundt and later by Blix and also Kulpe, Titchner, and especially Goldscheider. His aforementioned studies in 1882 led Blix to believe that pain was a specific sensation, but a year later he discarded this view. Goldscheider also shifted views: At first he did not believe that pain was specific, but by 1885, just as Blix was shifting in the other direction, Goldscheider came to the conclusion that the evidence was in the favor of specificity. He held his view until 1991 when he shifted once more because of the results obtained by Naunyn two years earlier, which led the latter to conclude that pain was the result of summation. In 1894 Goldscheider fully developed the theory that stimulus, intensity, and central summation were the critical determinants of pain. This was the first variant of the intensive theory which was to be followed subsequently by other theories called “patterned” and “summation” theories, all of which proposed that the particular pattern of nerve impulses that evoked pain were produced by the summation of the skin sensory input into the dorsal horn.
Thus, by the end of the 19th century, there existed three conflicting concepts on the nature of pain. The specificity theory and the intensive theory, which were in opposition to each other, were embraced by physiologists and a few psychologists. These two theories opposed the traditional Aristotelian concept that pain was an affective quality, which at this time was being supported by most philosophers and psychologists, including Lehmann in Germany, Bain, Bradley, Spencer, and Ward in England, and Baldwin, Dewey, James, and especially H. R. Marshall in America. The latter was the most active proponent of the pleasure-pain theorists and wrote extensively on the subject. During the decade between 1886 and 1895 there were proponents of each of these three theories who became involved in unprecedented, intensely fierce controversies. In an attempt to reconcile views of physiologists with those of philosophers and psychologists, Strong, then President of the American Psychological Association, in 1895 suggested that pain consisted of the original sensation and the psychic reaction or displeasure provoked by the sensation. This concept was later embraced by others, including Sherrington, who believed that pain was composed of both sensory and affective (feeling) dimensions.
During the first six decades of the present century, research on pain continued and the published data acquired were used to support either the specificity theory or the intensive theory or modification of these. The intense controversy between von Frey and Goldscheider continued until the late 1920s and each rallied supporters. Thus, we find Lugaro, Leriche, and subsequently Livingston, Nafe, Hebb, Weddell, and Sinclair, among many others, supporting the intensive theory, while Mitchell, Head, Adrian, Ranson, Waterston, Bishop, Sherrington, and Wolff and co-workers supported the specificity theory. Thus, the controversy continued, but by midcentury the theory of the philosophers had been wholly discarded and the specificity theory prevailed and became taught universally. (Research Publications: Association for Research in Nervous and Mental Disease 1-6)