Nocebo Hyperalgesia’s Social Transmission is Predicted by Synchrony

Nocebo Hyperalgesia

You may be familiar with the placebo effect, which is a positive result of a patient’s optimistic beliefs about a treatment. The “nocebo” effect describes the inverse, in which negative treatment expectations can lead to adverse side effects. Scientists have now discovered that an individual’s perception of pain during medical treatment can be intensified by observing how others react to the treatment, leading to a ripple nocebo hyperalgesia effect among others.

Hyperalgesia is defined as a heightened sensitivity to pain and an exaggerated response to it. It can happen when there is nerve damage or chemical alterations in the nerve pathways that are responsible for pain perception.

Pain is a complicated and nearly universal experience that combines psychological, cognitive, and social elements. Even though we commonly learn about suffering from others, the impact of social factors remains understudied.

A recent study has revealed that the nocebo effect can extend beyond the initial “harmful” experience, and that this is more pronounced when two people’s physiological reactions were more similar or “synchronized”—a phenomenon linked to stronger social bonds.

We found that expectations formed about a treatment can go on to influence both our self-perceived experience of that treatment as well as our physiological response to it,

said lead author Dr. Kirsten Barnes, from the School of Psychology at University of New South Wales Sydney.

These findings are relevant since treatments and therapy are frequently administered in community settings. Witnessing unpleasant experiences in group rehabilitation sessions or shared hospital wards, where patients may establish connections with one another, could be very detrimental.

Negative Treatment Experiences

Observing others is a major source of information regarding the adverse effects of medical intervention, such as increased pain. Dr. Barnes wanted to see if watching someone suffering the nocebo effect may drive negative expectations about that therapy to extend to another person, who then expresses a second nocebo effect, which transfers to someone else.

“Because if that’s the case, there’s the potential for the rapid propagation of these negative treatment experiences independent of any kind of active component of a treatment itself,”

said Dr. Barnes.

Dr. Barnes carried out the study while performing postdoctoral research at the University of Sydney, and it was authorized by the university’s Human Research Ethics Committee. The scientists recreated a scenario in the lab to determine whether a nocebo effect was being handed down through a chain of volunteers.

Prior to the experiment, participants were told that receiving a treatment on their arm would make them feel worse. This was further supported by a brief handout they were given to read while setting up the apparatus.

They were also informed that once the treatment was calibrated, they would be unable to feel it. Instead, a blue or green square would show on their computer screen to indicate whether the therapy was active or inactive, and they had to determine which was connected with treatment activity by demonstrating or watching.

Experiment Design

The first person, the demonstrator, was partnered with another subject to observe their responses to the treatment. This initial demonstrator was outfitted with a thermode, comparable to a little heat plate, that delivered a fast burst of heat to their skin. When the blue square was given, the intensity of the heat was increased, making it substantially more painful.

Next, the observer took over as the demonstrator, while a fresh participant was introduced to the experiment from the observer’s chair. The process was subsequently performed three times, each with a different observer.

Trial structure
Single trial structure presented simultaneously to Demonstrators and Observers within the same dyad. Credit: Commun Psychol 2, 33 Doi: 10.1038/s44271-024-00069-6 CC-BY

The participants had no idea that the treatment was a fake. While the level of the heat was secretly adjusted for the first demonstration, giving the impression that the treatment was beneficial, all other demonstrators received the same intensity regardless of whether they saw the green or blue square.

Interestingly, as each observer approached the demonstrator’s chair, several reported more pain when they saw the blue square, despite the fact that the level of the heat supplied to their arm was the same as when they saw the green square. These subjects were experiencing a nocebo effect because they believed the medication was active.

Response Measurement

The research group documented a variety of participant changes as this social interaction took place.

“We know that certain muscles in the face are activated during pain. We recorded activity in these muscles from both the demonstrator and observer when the ‘treatment’ was being delivered, so we could see how both were responding when they experienced or witnessed more pain to treatment,”

said Dr. Barnes. They also tracked the physiological response of both the demonstration and the spectator using their skin conductance—the sweat gland activity on their fingertips.

When they saw the blue or green square, the demonstrator was asked to self-report how much pain they were feeling, according to the team.

“After analyzing the results, we found that witnessing treatment-related pain exacerbated the observer’s own pain to a sham treatment, demonstrating that nocebo effects can be transmitted socially between people and passed successively along a chain.”

Interestingly, the participants showed genuine physiological changes in their skin conductance, and their pain-related facial expressions, when they thought that they were receiving treatment.

“This means that the nocebo effect is not just psychological, but can cause real changes in your body that alter the experience of pain,”

said Dr. Barnes.

Patient-practitioner Relationships

They also discovered that the more “synchronous” or similar the physiological responses of the demonstrator and observer were during the treatment session, the greater the nocebo effect of the observer when they later got the “treatment.”

Previous research suggests that a positive patient-practitioner relationship can result in better health outcomes.

“If you’re a patient in a group setting, such as participating in group therapy or experiencing an intervention for pain, it is generally believed that having social support is a good thing,”

said Dr. Barnes.

However, this study suggests that forming close relationships may, paradoxically, exacerbate pain if you witness someone having a bad treatment experience.

This work adds to a larger body of research that investigates how the social transmission of negative health information influences our health outcomes.

In a time when personal health experiences are frequently shared on social media and our social networks continue to grow, it is critical to comprehend the ramifications of this information, particularly in cases where it may incite unfavorable anticipations regarding the efficacy of treatments.

The findings of this study do not imply that there are no true active benefits of treatment, or that the pain you are experiencing is all psychological. However, if we can help to diminish these negative expectations, we may be able to reduce the nocebo effect and improve future patient experiences.

  1. Mostafa, R., McNair, N.A., Tan, W. et al. (2024) Interpersonal physiological and psychological synchrony predict the social transmission of nocebo hyperalgesia between individuals. Commun Psychol 2, 33 Doi: 10.1038/s44271-024-00069-6

Top image: Overview of the social transmission chain (blocks 1-3) Credit: Commun Psychol 2, 33 Doi: 10.1038/s44271-024-00069-6