Scientists have discovered that people with high levels of activity in a brain region called the right midfrontal gyrus (r-MFG) are particularly likely to respond to placebos when being treated for chronic pain. Publishing their work in the journal PLOS Biology, the researchers say their findings could enable clinicians to predict whether or not patients can be helped by sugary pills rather than actual medication, in order to devise personalized treatment programs.

The placebo effect is a strange and poorly understood phenomenon that highlights just how peculiar the human brain is. While studies have shown time and again that people often experience an improvement in symptoms when given fake medications, the mechanisms behind this psychosomatic trickery have yet to be illuminated.

In an attempt to figure how the brain regulates the placebo effect, researchers used functional magnetic resonance imaging (fMRI) to scan the brains of patients being treated for chronic knee osteoarthritis before administering a two-week course of placebo medication.

Half of these patients claimed they experienced a considerable reduction in pain levels during the trial, while the other half did not. This allowed the researchers to divide the group into placebo responders and non-responders.

Examining the MRI scans taken at the start of the trial, the study authors found that placebo responders all had higher connectivity in their r-MFG than non-responders, suggesting that this may be a reliable predictor of how likely a person is to benefit from a placebo.

^{Placebos can be effective at treating chronic pain, but only in some patients. wavebreakmedia/Shutterstock}

The team then conducted a second trial in which patients were once again subjected to a brain scan before being given either a placebo or a genuine painkiller called duloxetine, which they were instructed to take for three months.

At the end of the trial, the study authors were able to predict with a 95 percent accuracy which patients were most likely to have responded to the placebo, just by looking at the connectivity of their r-MFG. They also learned that connectivity levels in another brain region called the right parahippocampal gyrus (r-PHG) could be used to predict how well a patient would respond to duloxetine.

“The new technology will allow physicians to see what part of the brain is activated during an individual’s pain and choose the specific drug to target this spot,” explained study co-author Vania Apkarian in a statement. Essentially, this means that doctors may be able to use brain scans in order to decide whether to administer a placebo or an actual medication to a patient.

“Given the enormous societal toll of chronic pain, being able to predict placebo responders in a chronic pain population could both help the design of personalized medicine and enhance the success of clinical trials,” adds co-researcher Marwan Baliki.