Why Pain Doesn’t Always Mean Damage

A 29-year-old construction worker arrived at an emergency department with a six-inch nail sticking through his boot. He had jumped down onto it. Even a slight movement of the nail caused such intense pain that he had to be sedated, with fentanyl and midazolam, before doctors pulled it out.

But when they removed his boot, they found something unexpected. The nail had passed through the gap between his toes without piercing his foot. There was no injury at all (Fisher et al., 1995).

How could an uninjured foot hurt so much?

To answer this question, it helps to consider why pain exists.

Pain as a Protector

Pain is part of our body’s protective system. It's designed to prevent damage and harm to ourselves.

Imagine spraining your ankle while running a marathon. Without pain, you might continue running and make the injury worse or even cause permanent damage. Feeling pain prompts you to stop running, protect your ankle, and give it time to heal. In this case, pain has served its function.

Pain works like a smoke detector. It alerts us to possible danger so that we can respond.

But sometimes, the alarm goes off when we don’t need that protection.

Have you ever had your smoke alarm go off while cooking? Maybe you left your stir fry in the pan a bit longer than you should have. The next thing you know, the alarm is blaring, and you’re opening windows and fanning it to stop the awful sound. You may even feel annoyed because you had everything under control and didn't need the help of the smoke alarm.

The alarm has gone off, but it doesn’t mean there’s a fire.

The same is true of pain.

From Nerve Signals to the Experience of Pain

Let's take a look at how our bodies detect damage or risk of damage.

Nociception is how the nervous system detects and processes potentially harmful stimuli. It refers to the process of specialized nerve endings responding to things happening to our bodies, such as heat, pressure, or chemicals.

Nociception and pain are not the same thing.

Nociceptive signals are one piece of information the brain uses to make sense of what’s happening to us. The brain also draws on past experiences, expectations, emotions, and even social factors to "decide" what to do with those signals. One possible—but not the only—response is to generate pain, triggering protection.

You can think of nociception as an input and pain as a possible output.

Pain can also occur without a harmful stimulus, and it can persist on its own after an injury has healed (Butler & Moseley, 2013).

How is this possible? The answer has a lot to do with how our brains naturally work.

Our brains constantly make predictions based on what we’ve learned throughout our lives. For example, simply seeing a sliced lemon can make your mouth water before you’ve tasted anything. Your body is already responding to what it anticipates (Christensen & Navazesh, 1984).

What happens when the brain anticipates and predicts pain?

The following two studies show how suggestion and expectation can generate pain without a harmful physical stimulus.

In one experiment, researchers used hypnotic suggestion to induce the experience of painful heat while a probe against the skin remained at a non-painful 37°C. Participants reported pain, and brain scans showed activity in regions also involved in pain from physical stimulation (Derbyshire et al., 2004).

In another experiment, volunteers were connected to a device and told that its electrical current might cause a headache. Half reported pain, and pain ratings increased as researchers increased the machine’s settings. But the device was fake: it delivered no electrical current (Bayer et al., 1991).

The experience of pain was real and measurable even though the supposed cause—intense heat or electrical current—wasn’t there.

Putting It Together: Teaching the Brain to Turn Off Pain

Here’s a summary of what we’ve covered so far:

• Pain plays an important role in protecting us.

• Like a smoke detector, pain can sound an alarm even when there’s no injury.

• Nociceptive signals can contribute to pain, but they aren’t the pain experience itself.

• The brain can generate pain without a harmful stimulus, influenced by expectations, emotions, and learned experiences.

So what does this mean for chronic pain?

When learned responses keep pain going, we can work with the brain to change those responses. This may involve reducing fear of symptoms, changing expectations of pain, and developing new experiences of movement, sensation, and activity.

Understanding this opens up a different possibility: an approach to recovery that specifically aims to change how pain is generated by the brain.

Through understanding and consistent practice, the brain can learn that familiar sensations and activities are safe again. As those patterns change, significant pain reduction—and, for some forms of chronic pain, resolution—becomes possible.

References

Fisher JP, Hassan DT, O’Connor N. Minerva. BMJ. 1995;310:70. doi:10.1136/bmj.310.6971.70.

Butler DS, Moseley GL. Explain Pain. 2nd ed. Adelaide: Noigroup Publications; 2013.

Christensen CM, Navazesh M. Anticipatory salivary flow to the sight of different foods. Appetite. 1984;5(4):307–315. doi:10.1016/S0195-6663(84)80003-3.

Derbyshire SWG, Whalley MG, Stenger VA, Oakley DA. Cerebral activation during hypnotically induced and imagined pain. NeuroImage. 2004;23(1):392–401. doi:10.1016/j.neuroimage.2004.04.033.

Bayer TL, Baer PE, Early C. Situational and psychophysiological factors in psychologically induced pain. Pain. 1991;44(1):45–50. doi:10.1016/0304-3959(91)90145-N.