Why do we have pain?

Last time I wrote about how the brain controls pain. But why would the brain need a system to control pain? The answer is that although pain is unpleasant (at best!), it is often a valuable warning signal that forces us to take care of our bodies as we go about our business.

What would life be like without pain? We know the answer, because there are rare individuals who are born unable to feel pain. These children show what is known as “congenital insensitivity to pain.” Their parents need to be on constant alert, because the children can fall or cut themselves without being aware. They may bite their tongue or cheek or even break bones without knowing it.

One parent interviewed on public radio a few years ago highlighted how much we take pain for granted. She described how the preschool teachers needed to put ice in her daughter’s chili to cool it down to a safe temperature. Otherwise, the little girl could burn her mouth and esophagus. Unlike the rest of us, she did not automatically avoid swallowing food that was too hot. In a recent unfortunate case in Pakistan, a young boy without the ability to feel pain earned his living doing “entertainments” that involved such things as putting a knife through his arm. He died at age 14 after jumping off the roof of a building.

Less dramatic, but still important, people with diabetes often have reduced ability to detect painful stimuli to their feet, so they need to monitor their feet closely to make sure they don’t have sores or wounds.

These individuals highlight the importance of pain as a warning signal, but also draw attention to the suffering aspect of pain. Why does pain need to make us miserable? Because it motivates us to do something about the cause of the pain — to not eat that chili that is too hot. Pain helps us learn to avoid potentially injurious situations in the future. It might even send us to the doctor! This motivational aspect of pain is a fundamental part of our biology. Just as we are motivated to eat sweet foods or drink when we are thirsty, we are motivated to avoid things that cause us pain.

This brings us back to the original question: If pain is so important, why have a system to control it? There are two answers. First, there are times when it might be good to enhance sensitivity to pain. Such “hyperalgesia” can promote recovery by causing us to take extra care of an injured body part. As a possibly extreme example, you wouldn’t want to walk on a broken leg. Second, because pain is so effective at grabbing our attention, we may need to tamp it down in order to do something else important for survival – like run away from a bear, even if our leg is fractured. Less drastic swings in pain sensitivity can also be seen in daily life. If we are really hungry, we are more likely to endure a little bit of pain in order to get some food.

The reason for the pain control system then is that it gives us flexibility. It allows our brains to adjust our pain sensitivity so we can pursue other biological and psychological priorities when necessary, yet still maintain pain as a protective warning signal.

Mary Heinricher, Ph.D.
Professor, departments of Neurological Surgery and Behavioral Neuroscience
OHSU Brain Institute