Have you ever wondered why it is that your back hurts more when you are having a bad day? You would be forgiven for thinking that your back is “complaining”. In fact people talk about their backs being more bothersome when they are stressed. And it is probably true for most people that on a bad day their muscles are tighter and their joints a bit stiffer, if only because being stressed makes us more tense. However this is not the whole story. Your back might be bothersome, but the pain you are experiencing is constructed in the brain, 100%.
This is obvious when we think about phantom limb pain, pain which is experienced in a limb that has been amputated. Phantom limb pain occurs because the amputated limb is still represented in the brain in the somatosensory cortex, the part of the brain which locates where sensations are in the body.
The somatosensory cortex is stretched around the outer part of the brain running more or less from the crown of the head to a point level with the ear. As you can see from Fig 1, each part of the body is represented here, with larger areas devoted to the parts which are more sensitive such as the hands and lips. So in an amputee who has lost a leg, that leg is still represented on the somatosensory cortex and it is still possible for that leg section to fire up.
But why is the pain worse when you are having a bad day? This brings us to the pain matrix. For years scientists were trying to identify the part of the brain responsible for pain. But it remained elusive, because in fact it does not exist. Pain is a product of activity in a whole network of brain areas, which is known as the pain matrix. As you can see in Fig 2, the pain matrix is spread across a large part of the brain. When you hurt yourself – for instance by cutting your finger whilst chopping vegetables, information coming from the cut finger arrives via the spinal cord into the hindbrain (which is the most ancient part of the brain and is sometimes known as the reptilian brain). From here it fans out to the four corners of your brain. It is the excitation of all these areas which leads to the experience of pain and which gives it a particular character.
These areas of the brain all have other functions. Generally the areas on the outside of the brain, which is known as the cortex, are concerned with higher functions. For instance the prefrontal cortex is responsible for planning, empathy, emotional balance, intuition, morality and understanding; the anterior cingulate is concerned with emotional self-control, problem solving, and conflict detection and resolution, while the posterior cingulate is involved in autobiographical memory. The parts which are deeper inside the brain, which include the amygdala, hypothalamus and insula are concerned with more instinctual functions. So the amygdala and hypothalamus are concerned with the fight/flight response, emotional extremes and post traumatic stress. The insula is concerned with temperature, itch, disgust, pleasure, sensual touch and emotional self-awareness. It can actually help to calm the amygdala and it also connects emotion to bodily sensation, which is an important part of the experience of pain. How often have you been in so much pain that it made you cry?
There are other parts of the brain involved in the pain experience, but this is probably enough to be going on with. As you can imagine, the inputs of all these different areas help to give pain its emotional tenor. There is a saying that in any painful experience there are two arrows: the first arrow is the pain itself, the second arrow is the suffering that comes with it. It is often enough to get rid of the suffering for the pain to become tolerable and to interfere less with our daily lives.
In some conditions such as rheumatoid arthritis, some pain is inevitable. But it doesn’t have to be distressing. And it is not necessarily the case that the severity of the pain is equivalent to the severity of the injury. For instance you might have a mild case of arthritis in your hip but the pain is off the scale, while someone else might have severe arthritis and yet feel very little pain. Can you see how the involvement of so many brain centres can influence the extent of our pain? It is the stories we tell ourselves and our beliefs about pain which govern the severity of the pain.
Let’s take the case of two (imaginary) people with arthritic hips, Joe and Jim. Joe’s father had to have a hip replacement which was unsuccessful and he spent the last years of his life in a wheelchair. Joe knows that there are long waiting lists for operations and besides his doctor has told him that his hip is not bad enough yet to warrant surgery. So he is afraid that the pain will get worse and worse while he waits for the op and that he will end up in a wheelchair. Because of his fears about his hip, Joe does less and less and spends a lot of time thinking about his hip and worrying about it. The pain gets worse and worse and before long he is back at the doctor’s asking for stronger pain-killers.
Jim’s doctor has also told him that it is too early for a hip replacement. But Jim is happy about this because he doesn’t want to have surgery unless it is absolutely necessarily. Trevor, a colleague at work tells him that he was starting to notice some stiffness in his own hips and he took up Pilates to see whether he could improve their mobility. Jim decides to give the Pilates a try and Trevor suggests he comes along with him to his class. After a few weeks of Pilates, Jim’s hips are starting to loosen up a little and he notices that the pain has lessened as well.
Can you imagine how this plays out in Joe and Jim’s brains? Joe’s amygdala is probably over-active: he’s imagining what might go wrong and engaging his fight/flight response. Perhaps his posterior cingulate is busy examining those autobiographical memories about his father’s hip. On the other hand, Jim is benefiting from the activity of his anterior cingulate: emotional self-control and problem solving, as he looks for the best outcome given what his doctor has told him.
So if you are in pain, remember there is a sort of cerebral committee inside your head which is engaged in creating that pain and if you can listen more to the optimists and less to the pessimists, your pain will improve and with it your ability to live a fuller life.
The somatosensory homunculus: By OpenStax College Illustration from Anatomy & Physiology, Connexions Web site. https://cnx.org/content/col11496/1.6/, Jun 19, 2013.