Doctors' beliefs about treatment affect patients' experience

New research finds that the placebo effect may be socially contagious. In other words, a doctor's beliefs about whether or not a pain treatment will work can exert a subtle influence on how much pain the patient will actually experience.

Luke Chang — the director of the Computational Social Affective Neuroscience Laboratory at Dartmouth College in Hanover, NH — is the corresponding author of the new study.

Chang and colleagues have published their findings in the journal Nature Human BehaviourTrusted Source.

To study the phenomenon of socially transmitted placebo, the researchers devised three experiments. All three involved two different creams that were meant to relieve heat-induced pain by targeting pain receptors on the participants' skin.

One of the creams was called thermedol, and the other was a control cream. Although different in appearance, both creams were actually placebos — namely, petroleum jelly with no pain relieving properties at all.

The researchers asked undergraduate students to play the roles of "doctors" and "patients." They informed the "doctors" of the creams' benefits and conditioned them to believe that thermedol was better at relieving pain than the control cream.

The first experiment consisted of 24 "doctor-patient" pairs. In each pair, the "patient" did not know which cream was thermedol and which was the control. Only the "doctor" knew which was the "effective" cream.

The researchers then applied the creams to the participants' arms, followed by pain-inducing heat, in order to evaluate the effects of the cream. All participants received the same amount of heat.

During the experiment, all participants wore cameras that recorded their facial expressions in the doctor-patient interactions.

Using a machine-learning algorithm trained on facial signals of pain, the researchers were able to examine the effect of cues such as raised eyebrows, raised upper lips, or nose wrinkling on the perceived effectiveness of the treatments.

In this experiment, the participants reported experiencing less pain with thermedol, and skin conductance tests suggested that they actually did experience less discomfort. Their facial expressions also reflected less pain with thermedol.

Overall, across all three experiments, the results revealed that when the "doctors" believed that a treatment was effective, the "patients" reported feeling less pain. Their facial expressions and skin conductance tests also revealed fewer signs of pain.

The reasons for this remain unclear. However, the researchers believe that social contagion via facial cues is the most likely explanation.

"When the doctor thought that the treatment was going to work, the patient reported feeling that the doctor was more empathetic," says Chang.

"The doctor may have come across as warmer or more attentive. Yet, we don't know exactly what the doctor was doing differently to convey these beliefs that a treatment works. That's the next thing that we're going to explore," he adds.

"What we do know though is that these expectations are not being conveyed verbally but through subtle social cues," explains Chang.

Additional research, however, is needed to see how this plays out in the real world," he concludes.