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Jul 27, 2023

At Last, People Can Believe Your Pain

Woman holding head, looking down, doctor in background When visiting the doctor,

Woman holding head, looking down, doctor in background

When visiting the doctor, one of the first questions patients are asked about their pain is, "How badly does it hurt on a scale from 0-10?". While these pain ratings are a common method to help physicians diagnose chronic pain syndromes, they actually represent a significant barrier that doctors face in diagnosing and classifying symptoms of pain.

Chronic pain syndromes are one of the greatest healthcare problems worldwide, yet there is currently no objective method to measure either the neurophysiological causes or the severity of pain. In fact, self-reported pain symptoms are frequently dismissed as psychologically-based and left untreated. This especially affects women who are much more likely than men to receive sedatives rather than painkillers as treatment for self-reported pain symptoms. Research has shown that women who undergo coronary bypass surgery were only half as likely to be prescribed painkillers than men who receive the same procedure.

Now, a paper published in Nature Neuroscience suggests that we may be able to classify pain symptoms simply by examining a person's brain waves. This study may be the first step towards being able to diagnose chronic pain syndromes easily and objectively.

In the paper, Shirvalkar et al., discuss how they developed a brain implant and machine learning method to record patient brain waves in response to episodes of chronic and acute pain. Using their system, the researchers were able to successfully predict patient pain ratings, marking the first study to record regions of the human brain as a measurement of pain severity.

Previous attempts to identify biomarkers of pain have only focused on healthy participants. While important, these studies do not accurately depict the experiences of those who have chronic pain syndromes. Other studies have also measured pain using probes to detect brain activity. However, these probes have only been able to measure brain activity over short periods of time and cannot produce long-term measurements of brain activity.

With these limitations, Shirvalkar et al. were interested in using a novel probe called the Medtronic Activa PC + S to collect brain wave recordings of four human participants over long durations of time. The novel probe was implanted and allowed the researchers to measure participant brain waves over the course of 3-6 months.

Figure 1: X-ray image of participant with implanted brain wave monitor.

The first step was to determine each participant's baseline brain activity in the brain's pain regions. The researchers were particularly interested in examining the activity of two regions: the rostral anterior cingulate cortex and the orbitofrontal cortex. The rostral anterior cingulate cortex is known to play a role in emotional processing during pain. The orbitofrontal cortex has rarely been studied in pain but is connected to several other regions of the brain related to pain. Due to these connections, Shirvalkar et al. speculated that the orbitofrontal cortex may be an essential region of the brain for pain perception.

To determine whether the sensor could accurately record pain severity in the participants, the researchers asked each participant to provide pain ratings multiple times over the course of each day for 3-6 months. The researchers then compared these pain ratings to the brain wave activity collected each day to determine how the brain activity correlated to the pain ratings of each participant.

From these results, researchers found that they were able to predict the pain states or pain ratings of each participant by observing the activity of the orbitofrontal cortex alone.

This left an interesting question, could the sensor also predict the pain intensity of induced immediate pain?

To test this, the researchers applied a heated probe to each participant. The probe was placed on the most painful region on each participant's body affected by chronic pain as well as the same body part on the unaffected side. For example, if a participant experienced chronic pain in their right leg, the heat probe would be applied to both the right leg and the left leg.

After applying the probe, participants reported on the pain intensity while the researchers observed each participant's brain wave activity. Interestingly, the orbitofrontal cortex did not accurately measure the pain severities caused by the heat probe, suggesting that the anterior cingulate cortex may be more involved with acute pain than the orbitofrontal cortex.

Overall, this study represents significant progress in developing an objective metric to track pain severity. While more work must be done to determine a less invasive measure of chronic pain, this work brings us one step closer to improving pain diagnoses and hopefully, providing better care for those who experience chronic pain syndromes.