We feel your pain

Pain has always been a notoriously private and subjective experience, but a team of US medical researchers now appear to have found a way to detect it objectively using functional NIR spectroscopy. This opens up the possibility of being able to tell whether or not patients who are unable to communicate, such as young infants or those who have had a stroke, are in pain.

Functional NIR spectroscopy determines blood flow in the brain, as a proxy for brain activity, by measuring changes in haemoglobin concentrations. Researchers from Harvard Medical School (HMS) and Boston Children’s Hospital, led by Meryem Yücel at HMS, wondered whether a painful sensation would cause a detectable change in blood flow in certain regions of the brain.

To find out, they used functional NIR spectroscopy to monitor haemoglobin concentrations in both the frontal cortex and the somatosensory cortex of 11 male volunteers exposed to either an innocuous or painful electric shock. As they describe in Scientific Reports, this involved using a probe comprising 11 NIR sources and 27 detectors attached to the volunteers’ heads to measure NIR spectra at wavelengths of 690nm and 830nm.

The researchers discovered that while the innocuous shock didn’t cause major changes in haemoglobin concentrations in either cortex, the painful shock did produce detectable changes after a few seconds in all 11 volunteers, although only in the somatosensory cortex. Furthermore, these concentration changes became less pronounced if the shock was repeated after three minutes, demonstrating the well-known habituation process that can cause a stimulus to become less painful when repeated.

This study needs to be conducted in a lot more volunteers, especially female volunteers, and with other painful stimuli, such as heat, to determine whether this change in blood flow is truly a universal response to pain. If it is, though, no one will again have to suffer their pain in silence.

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