Pain can be a symptom. Pain can be a disease. Pain can be mysterious and hard to figure out. In fact, we still don’t completely understand what happens in the brain when you stub your toe although we know it’s complicated.

How complicated? Take the example of the soldier shot in battle who rescues his buddy and feels no pain until safe. Or imagine you have just stubbed your toe and at the same time you see your child hit by a car. I doubt you’d feel a lot of pain in your toe but you’d be frantic about your child. Obviously something must happen in the nervous system that prevents the brain from processing signals from the injured part to create the feeling of pain.

In these examples a crucial ingredient is the emotional bond between parent and child or soldiers in war. If it was a squirrel instead of your child you saw hit by a car your reaction would probably be quite different. It makes sense to say that an emotional response – and emotion is a function of the brain – has affected a pain response in the situations above.

There is a wealth of research showing differences among people in response to pain depending upon culture and early experience with pain. This suggests that learning modifies our feeling of pain. We also know that learning changes the physical structure of the brain and this may be a clue as to how learning (and perhaps other neurological processes) can affect pain.

Although different parts of the brain have different functions, they interact with each other. In some cases one part can take over another part’s function, so closely connected are they. It follows that what affects one part of the nervous system can affect all parts, at least in some circumstances. It may therefore be that the experience of pain depends on whatever else is going on in the brain. This is very complicated indeed.

From the preceding, the picture of pain that emerges is that of a complex phenomenon involving factors to do with the nerves, learning, memory and emotions. It is no wonder that treating pain is still such a big challenge.