Opioid receptors in brain affect reaction to another person’s pain

Image by P. Simonau

Watching someone else suffering from pain is distressing. What mechanisms cause that distress? And why do some of us experience it more strongly than others?

A new Finnish research study has now demonstrated that seeing others in pain activates the same brain regions involved in firsthand pain, which suggests that a shared neuromolecular pathway processes both types of pain. Specifically, the researchers showed that the endogenous opioid system, but not the dopamine system, contribute to vicarious pain.

The endogenous opioid system is a set of neurons in the brain that naturally produces opioids to help modulate emotions and pain. Similarly, the dopamine system consists of neurons that synthesize and release dopamine, which helps manage motor control, pain, reward and addictive behaviors. So both of these systems are known to play an important role in processing firsthand pain, but their role in vicarious pain was unexplored.

The research team conducted the study by imaging 35 healthy women ranging in age from 19 to 58 years old. First, they performed two positron emission tomography (PET) studies on different days using radiopharmaceuticals that quantified the availability of opioid and dopamine receptors in each woman’s brain to better understand the individual opioid and dopamine systems. Next, they investigated how each woman responded to vicarious pain by performing a functional MRI scan while she watched videos of humans experiencing painful and painless situations.

The researchers found a negative correlation between opioid receptor availability and response to vicarious pain — women with less opioid receptors reacted more strongly to seeing someone else’s distress, as recently reported in Cerebral Cortex. In contrast, they found no correlation with the dopamine receptor availability.

The authors concluded in the paper, “These results suggest that the opioid system contributes to neural processing of vicarious pain, and that interindividual differences in opioidergic system could explain why some individuals react more strongly than others to seeing pain.”

This is a reposting of my Scope blog story, courtesy of Stanford School of Medicine.

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