You expect to feel pain when you fall off a bicycle but should you feel pain when you see someone else do the same? Some people do because pain is more than the actual injury; it’s a perception.
For some, witnessing or imagining another person’s injury can trigger an experience of pain similar to when they injure themselves. It’s called pain synaesthesia, but why does it happen?
When we hurt ourselves, messages are sent to our brain to say the body has suffered an injury. This message is sent to regions of the brain called the pain matrix.
The different areas of the pain matrix process parts of the injury. For example, sensory brain regions process the location and intensity of the pain; whereas affective brain regions deal with the unpleasantness of the pain and whether you need to run away or protect yourself.
But these brain regions don’t just activate when we hurt ourselves. They are also active when we witness another person experience pain.
These regions that appear to mimic actual experiences are described as “mirror systems”.
Mirror systems are thought to impact how we understand the actions and emotions of others. For example, we normally don’t experience disgust when we see another person disgusted but the same areas of our brain activate as if we were, allowing us to understand the experience.
So what stops us from experiencing disgust or pain as our own if the same reactions occur in the brain? The answer may lie in the inhibition of mirror systems. When the mirror system is working, the brain is able to differentiate between your experiences and another’s.
We suggest that when mirror areas involved in processing pain become hyperactive, inhibitory mechanisms are unable to work. As a result, observing an injury activates the brain as if we were in the other person’s shoes (so to speak), causing the experience of pain. This experience is pain synaesthesia.
When we first started our research, we found it was an experience documented most commonly among amputees who experienced pain in their missing limb. In fact, around 16% of amputees experience synaesthetic pain.
But it is not just found in amputees. People within the general population (who have not had significant pain in the past) experience pain synaesthesia as well.
The fact that this experience can occur in different people for different reasons suggests there are multiple ways for the mirror systems in the brain to become hyperactive.
One reason may be through pain-related trauma, such as that experienced by amputees. Another reason may be abnormal connections in the structure of the brain, e.g., extra connections between visual and pain areas. Or possibly that the function of otherwise normal processes have become altered.
At this point, we don’t know why people experience synaesthetic pain. What we do know is that when people who experience synaesthetic pain see another’s injury, their brains respond differently to people who do not experience it.
At the moment, we are still investigating pain synaesthesia, but knowing more about synaesthetic pain may help us better understand how people perceive pain, how they recognise other people’s physical and emotional states, and how these perceptions can change over time.