Mindfulness Meditation and Placebo Modulate Different Brain Patterns To Reduce Pain

According to a new study, not only does mindfulness meditation reduce pain more than a placebo, but it also uses different neural patterns when reducing pain, indicating that it is not acting through the placebo effect. Published in Biological Psychiatry, the study was funded by the National Center for Complementary and Integrative Health and conducted by researchers from the University of California San Diego and Dartmouth College.

The placebo effect has been shown to engage brain mechanisms that modify beliefs, expectations, and conditioning to reduce a person’s experience of pain. Several clinical trials suggest that mindfulness meditation can lead to lasting improvements in chronic pain, and this effect has been thought to occur through activation of the placebo response. However, this new study, which paired functional magnetic resonance imaging (fMRI) with a type of supervised machine learning called multivariate pattern analysis (MVPA), showed that mindfulness meditation in fact evokes pain neural patterns, or signatures, in a way that differs from the placebo effect.

The researchers combined datasets from two previous clinical trials that both used advanced brain imaging techniques. Out of a total of 115 healthy participants across the two trials, 37 were randomly assigned to a mindfulness meditation group, 20 to a sham-mindfulness meditation group, 19 to a placebo-cream group, and 39 to a book-listening group. All four groups participated in four 20-minute intervention sessions. 

In the mindfulness meditation group, participants were taught to focus on changing the cadence of their breath and to refocus on their breath when they were distracted. They were also taught to reduce self-judgment by acknowledging without reaction their arising thoughts, feelings, and emotions. Participants in the sham-mindfulness meditation group were led to believe they were practicing mindfulness meditation but were not instructed to mindfully focus on their breath in a nonjudgmental way. In the placebo-cream group, participants received noxious heat stimuli to the back of the calf followed by application of a placebo cream that participants were told was effective at reducing pain. The book-listening group listened to an audio book. 

After the four sessions, all participants underwent noxious heat testing (application of a painful but harmless heat stimulus to the back of the leg) during fMRI. The researchers evaluated how pain ratings and brain imaging pain signatures were affected by the interventions. Three specific brain imaging pain signatures were analyzed: the Neurologic Pain Signature (NPS), which tracks pain intensity brought on by noxious stimuli and is mostly insensitive to placebo; the Negative Affective Pain Signature (NAPS), which is linked to the negative emotions around pain; and the Stimulus Intensity Independent Pain Signature-1 (SIIPS-1), which involves placebo-related factors such as expectations for relief, conditioning, perceived control, and psychosocial contexts.

The analysis indicated that mindfulness meditation significantly reduced NPS and NAPS responses whereas the other three interventions did not. Also, the placebo cream significantly reduced SIIPS-1 responses when compared to the other three interventions. And while sham-mindfulness meditation significantly increased SIIPS-1 responses, neither mindfulness meditation nor the book-listening intervention modulated SIIPS-1. 

Sham-mindfulness meditation and placebo cream significantly reduced pain when compared to the book-listening intervention, and the two did not differ from each other on ratings of pain intensity and pain unpleasantness. However, mindfulness meditation was found to be more effective at reducing pain than all three other interventions, both in pain intensity and pain unpleasantness ratings. 

According to the researchers, the findings provide new evidence that mindfulness meditation impacts the sensory and more emotionally aligned dimensions of the pain experience. The results of this study suggest that the brain systems underlying pain relief by mindfulness meditation and placebo are distinct and do not overlap. However, it will take more research to show whether the effects demonstrated in this study occur in people with chronic pain as well as in healthy people.