Brain scans – swimming up a muddy stream to measure pain.

Neil Pearson

A recent media report started with a statement paraphrased as follows: “Scientists report that they have developed a way to measure how much pain a person is having by scanning their brains”. The writers went on to say that, when doctors are faced with someone in pain, they have no way to judge its severity other than to ask questions.

If you are like me, such statements are worse than nails on a chalk board. Yet the report quotes one of the researchers as saying that children and people with cognitive impairments often cannot express their pain. Being able to measure it would help provide better treatment.

Again, if you are like me, you don’t like to be misled. So here is more information on the study, which will help you understand it better.

This is a study of how brain activity changes when a hot stimulus is applied to the skin. In other words, the scientists studied acute pain. Therefore, if the pain is chronic and not acute, we should not assume any similar findings.

I recall reading evidence that people who volunteer for studies in which they will experience pain might have important differences from people who would not volunteer for this. Of course, since it is ethically not acceptable to study pain in people without their consent, we will never fully sort this hypothesis out, but we need to keep it in mind.

The study found a different pattern of brain activity when the person reported that the sensation was warm compared to when the person said it was painful. The brain scan also showed different activity with social pain (i.e. emotional pain) versus heat pain (i.e. physical pain). However, it was harder to tell the difference between these two situations than to identify whether the person felt warmth or pain from heat.

The research showed the same increased brain activity remained but was less intense when the subject was given a pain killer, Remifentanil.

The research in the study did not have anything to do with measuring pain severity. It is important to note is that a brain scan cannot show how much pain a person has! Pain is much too complex for anyone to expect that an fMRI scan will provide accurate information about pain intensity.

So what can we learn from this study? For a start, it confirms what most people believe. When we experience acute pain, many parts of the brain have altered activity versus when we do not have acute pain. We know this of chronic pain too. The study also tells us that there are similar brain patterns whether we are suffering from something we call physical pain versus emotional pain. We know this too from studies comparing brain changes in chronic pain to those in depression.

The study also tells us that, although there are individual differences in brain activity when we experience acute pain, there is an identifiable pattern of brain activity with similarities across people. This will be an interesting advance to this research, since many health professionals have noted both similarities and differences in pain across individuals and across quite varied pain conditions. This might mean that for each pain condition there will be a core set of treatment options specific to that condition, and another set of options that will be effective across pain conditions and individuals.

There are two other extremely important considerations to take into account when looking at this research. One, brain scans are not precise and are not without errors. As such, any suggestion that they can be used to prove a person has pain should be shut down immediately. To provide some proof of this imprecision, other researchers conducted the following experiment: One mature Atlantic salmon, approximately 18 inches long and not alive at the time of brain scanning, was shown a series of photographs showing human individuals in emotionally charged social situations. The salmon was asked to identify the emotion in the photo while an fMRI scanned for brain activity. In the scan results, the dead salmon’s small brain depicted signs of activity, and it appeared that the salmon was actually thinking about the pictures it was shown. Did I mention that the salmon was already dead at the time?!

This experiment, of course, does not mean that we cannot rely at all on fMRI findings, but we should recognize that they are far more useful as experimental tools rather than clinical ones. As such – which brings us to our second consideration – it is imperative that we spend more time thinking about what we think about pain. If someone opines that we can measure pain precisely by looking at brain activity, then we are seeing pain solely as a medical condition, or worse. We know we cannot measure the electrical activity in a muscle and predict how much force it is creating. The nerve activity in the brain is vastly more complex, so why would we reckon we can succeed there?

Pain is a human experience. Would a brain scan enable us to prove how in love a person is with someone else?

1. An fMRI-Based Neurologic Signature of Physical Pain. Tor D. Wager, Ph.D., Lauren Y. Atlas, Ph.D., Martin A. Lindquist, Ph.D., Mathieu Roy, Ph.D., Choong-Wan Woo, M.A., and Ethan Kross, Ph.D. N Engl J Med 2013; 368:1388-1397

  • Neil Pearson combines the practical applications of pain care while teaching through his retreats, pain management products and resources to provide guidance in recovery from chronic pain.
  • [tags] fMRI, brain, scan, pain, understanding, measure, study, [/tags]

    Author: Neil Pearson

    Neil Pearson is a yoga therapist, physical therapist and Clinical Assistant Professor at UBC. He provides therapy exclusively for people with complex pain problems. Neil shares his knowledge of anatomy, physiology, pain and pathophysiology through

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