The way I see it:

This sentence is the one that stayed with me for days, and somehow, summarises the relevance of this article by Nicola Twilley: "only you feel your pain". 
Pain, although it’s a physiological process, is one of the most subjective ones, not only difficult to explain, but to measure.There are specific neural regions that are activated with the experience of pain, with the memory or anticipation of pain, but the intensity of how we experience it, really depends on each person, and the circumstances that have surrounded, or surround or painful experience. Some food for thought.

Compilation:

For scientists, pain has long presented an intractable problem: it is a physiological process, just like breathing or digestion, and yet it is inherently, stubbornly subjective—only you feel your pain. It is also a notoriously hard experience to convey accurately to others.

Elaine Scarry, in the 1985 book “The Body in Pain,” wrote, “Physical pain does not simply resist language but actively destroys it.”

The result, published two decades later, was the McGill Pain Questionnaire, a scale comprising some eighty descriptors—“stabbing,” “gnawing,” “radiating,” “shooting,” and so on.

Other basic sensory perceptions—touch, taste, sight, smell, hearing—have been traced to particular areas of the brain. “We don’t have that for pain,” she said. “We still don’t know exactly how the brain constructs this experience that you absolutely, unarguably know hurts.”

The anterior insula and the prefrontal cortices. These areas, Tracey and Ploghaus concluded, must be responsible for the anticipation of pain.

Showing that the experience of pain could be created in part by anticipation, rather than by actual sensation, was the first experimental step in breaking the phenomenon down into its constituent elements.

If faith engages a neural mechanism with analgesic benefits—the Catholics showed heightened activity in an area usually associated with the ability to override a physical response—it may be possible to find other, secular ways to engage that circuit.

In 2013, Tor Wager a neuroscientist at the University of Colorado, Boulder, took the logical next step by creating an algorithm that could recognize pain’s distinctive patterns; today, it can pick out brains in pain with more than ninety-five-per-cent accuracy.

There is only one region that is consistently active at a high level: the dorsal posterior region of the insula.

Recently discovered that the intensity of a prolonged painful experience corresponds precisely with variations in the blood flow to this particular area of the brain. In other words, activity in this area provides, at last, a biological benchmark for agony.

“There’s a Jeremy Bentham quote I like,” Tracey said. “ ‘Nature has placed mankind under the governance of two sovereign masters, pain and pleasure.’ These are the two things that drive us, as animals, to do what we do.”

Chronic pain is often defined, somewhat misleadingly, as “pain that extends beyond the expected period of healing.

In reality, once you’ve “gone chronic,” as Tracey puts it, pain is the disease, rather than a symptom.

A key neural mechanism of chronic pain. It is situated in the brain stem, a hard-to-reach, tube-shaped mass of gray matter at the top of the spinal cord, which functions as the conduit for communication between the brain and the body.

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