TBS Modulates Placebo, Nocebo Experiences

Kate Johnson

May 11, 2021

Noninvasive transcranial brain stimulation has the potential to boost a patient's placebo experience or blunt the nocebo experience, according to results of a new study published in the Proceedings of the National Academy of Sciences (PNAS).

"Placebo and nocebo effects are a critical component of clinical care and efficacy studies," said senior author Jian Kong, MD, associate professor in the department of psychiatry at Massachusetts General Hospital, Charlestown campus. "Harnessing these effects in clinical practice and research could facilitate the development of new pain management methods," he said. "Healing may involve multiple components: the self-healing properties of the body; the nonspecific effects of treatment (i.e., placebo effect); and the specific effect of a physical or pharmacologic intervention. Therefore, enhancing the placebo effect may ultimately boost the overall therapeutic effect of existing treatment," he explained, emphasizing that the results are preliminary and should be interpreted with caution.

The authors noted that reducing nocebo effects could also be a major benefit "since patients discontinue prescribed medications, make unnecessary medical visits, and take additional medications to counteract adverse effects that are actually nocebo effects."

Testing the Hypothesis

The randomized, double-blind, sham-controlled study used transcranial direct current stimulation (tDCS), which delivers an electrical current to the brain via scalp electrodes. The aim was to see if stimulating the dorsolateral prefrontal cortex with tDCS could alter the brain's perception of placebo and nocebo experiences.

The study included 81 participants (37 females, mean age: 27.4 years), who were randomized into one of three tDCS groups (anodal, cathodal, or sham).

All participants were first conditioned to believe that an inert cream was either lidocaine or capsaicin and that this cream could either dull the impact of a painful heat stimulus (placebo analgesia) or exacerbate it (nocebo hyperalgesia). Participants were then placed into a functional MRI scanner where tDCS was initiated. Painful stimuli were then applied to spots on their forearms where they believed they had either lidocaine, capsaicin, or a neutral control cream and they rated the pain using the Gracely Sensory Scale.

Placebo analgesia was defined as the difference between perceived pain intensity where participants believed they had lidocaine cream compared with where they believed they had control cream. Nocebo hyperalgesia was defined as the difference between perceived pain intensity where they believed they had capsaicin cream compared with where they believed they had control cream.

The researchers found that compared with sham tDCS, cathodal tDCS showed significant effects in increasing placebo analgesia and brain responses in the ventromedial prefrontal cortex (vmPFC), while anodal tDCS showed significant effects in inhibiting nocebo hyperalgesia and brain responses in the insula.

"The potential to enhance salubrious placebo effects and/or diminish treatment-interfering nocebo effects may have clinical significance," the authors noted. "For example, clinical studies have suggested that expectancy is positively associated with chronic pain improvement, and using conditioning-like expectancy manipulation, we have shown that significantly boosting expectancy can improve treatment outcome."

Proof of Concept

Asked to comment on the study, Brian E. McGeeney, MD, of the John R. Graham Headache Center at Brigham and Women's Faulkner Hospital in Boston, said "the findings are a proof of concept that it is possible to use noninvasive brain stimulation to modulate placebo and nocebo pain effects."

Although the findings do not have immediate clinical application, they are "exciting" and "break new ground in expectancy research," he said.

"It is important to recognize that the researchers are trying to utilize a purported expectancy mechanism rather than attempting to alter placebo/nocebo by verbal and other cues. It remains to be seen whether the manipulation of brief experimental pain like this can translate into altered chronic pain over time, the main clinical goal. Current tDCS therapy for various reasons is necessarily brief and one can ask whether there are meaningful changes from brief stimulation. Such results can foster speculation as to whether direct strategic placement of intracranial stimulation leads could result in more longstanding similar benefits."

Kong holds equity in a startup company (MNT) and a pending patent to develop new peripheral neuromodulation tools, but declares no conflict of interest. All other authors declare no conflict of interest.

This article originally appeared on MDedge.com, part of the Medscape Professional Network.

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