When we think about pain, we tend to think of signals being sent from one part of our body to the brain, to alert it of a problem. What many people fail to realise is that this is a two-way system, and there are also signals that travel from the brain and down the spinal cord. These signals determine our levels of sensitivity, and therefore determine “how much” pain we feel. In simple English, pain is not just a result of the problem, it also comes from how sensitive we are in general.
The sensory neurons that detect an injury or risk are known as nociceptors, and these are essentially what we feel when we feel pain. Nociceptors travel along a number of pathways depending on where the pain originates, and the makeup of this path can cause different people to experience pain in different ways. For example, pain can travel from the skin, through the cells, up the spinal cord, and into the brain.
The first point at which our experiences with pain can diverge from one another is the very beginning. The nociceptors in some people are just naturally more responsive than in others, and can respond differently to different types of stimuli - e.g. some people will be very sensitive to touching something hot, but more capable of withstanding physical trauma. This can be shaped over time by our experiences in life, as our bodies determine what should be considered a threat and what should not. For example, this is one reason a boxer can shake off a powerful punch to the face: on some level, their body knows they are not in fatal danger.
But the level of pain we feel is not just about what we are perceiving, but also what we are not perceiving in that moment. Nociceptors travel up the spinal cord via the small fibres, while other sensory information (such as pressure) travel up the large fibres. According to the gate-control theory of pain, when these signals reach the spinal cord, it acts as a sort of gate, deciding which information and how much of it to let through to the brain. The gate-control theory states that by inundating the large fibres with information, we can drown out the signals travelling along the smaller fibres.
Finally, when the signals do reach the brain, how they are perceived will be affected by the state of the brain itself. This has proven to be a bit of a challenge to study, as there are so many factors in how our brain functions. A younger brain may experience pain sooner than an older brain, but the pain may also pass faster. Or, an older person may have developed a higher threshold for pain throughout their life, and may not register the pain to the same degree. On the other hand, the effects of ageing could reduce a person’s ability to regulate their pain inhibitors, and leave them more susceptible to receiving nociceptors. An individual’s emotional state can also have an effect, with people who are stressed, anxious, or depressed being much more responsive to any sort of stimuli.
The study of pain has always been a priority for medical science, and yet there is still so much we don’t know about it. Part of this is because there is not always something physical like a wound to examine, but part of it is because much of the science depends on what the patients are telling us, and nobody can ever truly compare their level of pain to someone else’s. We do know that it varies from person to person, and that there are a lot of factors that can affect how we feel pain. While the cause of the pain does of course have an effect, the science is increasingly showing that psychological factors are the dominant component in determining how that pain is perceived.