Where is your pain?
The short answer is simple: in your brain. It may seem as if it’s in your broken finger, or the toe you just stubbed on the door, or in your aching tooth. But it’s not. Pain is a sensory experience, and resides in your brain.
To consider why I say that, ask yourself: does an anesthetized patient feel pain during a surgical procedure? The answer (assuming the patient is properly anesthetized of course!) is that he or she feels no pain. Yet surgery always involves some degree of tissue damage. In the days before anesthesia, patients generally avoided surgery at almost all costs, and most procedures were horribly painful. (Anyone who has read the seventeenth century Diary of Samuel Pepys cannot forget his description of being trussed up for an excruciating surgical procedure that he underwent for removal of bladder stones. Modern surgery would not be possible without anesthesia.)
What this little thought experiment reminds us is that pain is not the same thing as injury. You can sustain an injury (or undergo a surgical procedure), but unless your brain processes that information, there is no pain. Pain, by definition, is a conscious experience.
Given that pain happens in our brains, it might seem as if pain could be eliminated very easily if only we could somehow block activity in the brain’s “pain center.” Unfortunately, it is not as simple as that. Most important, there is no focal point, no “center” for pain in the brain. There is no one region that specifically produces pain when stimulated, no one region that can be lesioned to eliminate pain permanently.
Instead, information about injury is processed across a network of brain regions sometimes referred to as the “pain matrix.” Different nodes in this matrix seem to play various roles in the pain sensation. Some parts of the brain seem to be more important for processing the location or degree of injury. That is, they let you know that it’s your finger, not your toe, and tell you how bad it is. Other parts of the brain contribute to the emotional and cognitive aspects of the pain sensation. For example, elements of the pain matrix that include the frontal lobes of the brain are important for the suffering element of pain and for evaluating its significance for our lives. (Will I be able to work after this injury? Does this mean my cancer is coming back?) This appraisal of how an injury and its consequences fit in with a person’s overall experience is an important part of pain.
Any sensation of pain therefore arises not from the activity of a “pain neuron” or “pain center,” but reflects activity distributed across a wide brain network. This can make pain management extremely complicated. But approaches to pain treatment that take the distributed nature of pain processing into account have more hopes of succeeding. It’s a very big topic – and one that I’ll be touching on over the coming months.