Pain 101: A History of the Different Types of Pain
In order to determine how to treat pain, you need to start by understanding its causes. Starting from the beginning, pain has long been considered to be one of the sub-functions of the sense of touch1.
Descartes’ classic picture of pain provided a framework for the early anatomists to explain how pain is detected and relayed to the spinal cord and brain. Descartes wrote, “If, for example, fire comes near the foot, minute particles of this fire, which you know move at great velocity, have the power to set in motion the spot of skin on the foot which they touch, and by this means pulling on the delicate thread which is attached to the spot of the skin, they open up at the same instant the pore against which the delicate thread ends, just as by pulling on one end of a rope one makes to strike at the same instant a bell which hangs at the end.”2
Early descriptions of the pain pathways in humans consisted of relatively simple connections from the primary nociceptor (the peripheral nerve) to spinal cord to thalamus and finally terminating in cerebral cortex. However, even by the early 20th century the view of pain as being transmitted via “hard-wired” circuits was starting to be questioned.
In 1911, Head and Holmes observed that patients with specific cerebral lesions, particularly those in the parietal lobe disrupting primary somatosensory cortex, were still able to feel pain. This was an unexpected finding given that the sensory portion of the thalamus was thought to project exclusively to this region.3
Advances in immunohistochemistry, histology, genetics and neuroimaging, however, have challenged these earlier theories. Currently, the explanation of pain has been dramatically modified from the one-to-one correspondence of receptor to specific pain, to a more plastic and integrative model.4
So now that we understand more about pain and the history of how we've understood it, let's talk about how we diagnose it today. To start, pain perception (or nociception) is a complex phenomenon5. Pain can be broadly classified into the following categories:
Nociceptive pain is generally protective because it prevents further injury and/or promotes healing. Normally, pain is produced only by intense stimuli that are potentially or actually damaging to tissue. This pain is mediated by a specific system of high-threshold peripheral and central neurons designed to respond only to such noxious stimuli (the nociceptive system) that is responsible for pain experienced in response to a needle prick or touching a hot surface. Nociceptive pain is an essential warning device that helps protect from harmful stimuli in the environment6.
Inflammatory pain has no protective function, and results from tissue damage (e.g., trauma, surgery, rheumatoid arthritis).
Neuropathic pain results from direct injury or dysfunction of the nervous system, (e.g., post herpetic neuralgia, diabetic neuropathy).
Functional pain (as occurs in fibromyalgia and irritable bowel syndrome) is associated with abnormal neural processing in the absence of neurologic disease or peripheral abnormalities. There is usually an overlap among the different pain states.
When your doctor gives you treatment advice, she will typically start by determining the root cause of your pain, and then will determine a course of treatment that she deems most appropriate. This can include a wide variety of options, from drugs to surgery to natural options such as the Energeze Patch. Check back next time to learn more about pain treatment and where it might be heading in the future!
- Kandel E, Schwartz JH, Jessell TM. 2000. Principles of Neural Science (International Edition) New York: McGraw-Hill.
- Descartes R.1644 Lectures on the History of Physiology During the 16th, 17th and 18th Centuries. Cambridge: Cambridge University Press, L’Homme.
- Head H, Holmes G. 1965. Sensory disturbances from cerebral lesions. Brain Res. 34(1911):102–254.
- Melzack R, Wall P. 1965. Pain mechanisms: a new theory. Science 150:971–999.
Woolf CJ. 2004. Pain: moving from symptom control toward mechanism-specific pharmacologic management. Ann. Intern. Med. 140:441-451.
Gibson SJ, Farrell M. 2004. A review of age differences in the neurophysiology of nociception and the perceptual experience of pain. Clin J Pain 20(4):227-39.