Abstract
IntroductionTactile stimulation during a placebo treatment could enhance its credibility and thereby boost positive treatment expectations and the placebo effect. This experimental study aimed to investigate the interplay between tactile stimulation, expectation, and treatment credibility for the placebo effect in nausea.MethodsNinety healthy participants were exposed to a 20-min vection stimulus on two separate days and were randomly allocated to one of three groups on the second day after the baseline period: Placebo transcutaneous electrical nerve stimulation (TENS) with tactile stimulation (n = 30), placebo TENS without tactile stimulation (n = 30), or no intervention (n = 30). Placebo TENS was performed for 20 min at a dummy acupuncture point on both forearms. Expected and perceived nausea severity and further symptoms of motion sickness were assessed at baseline and during the evaluation period. At the end of the experiment, participants in the placebo groups guessed whether they had received active or placebo treatment.ResultsExpected nausea decreased significantly more in the placebo groups as compared to the no treatment control group (interaction day × group, F = 6.60, p = 0.003, partial η2 = 0.20), with equal reductions in the two placebo groups (p = 1.0). Reduced expectation went along with a significant placebo effect on nausea (interaction day × group, F = 22.2, p < 0.001, partial η2 = 0.35) with no difference between the two placebo groups (p = 1.0). Twenty-three out of 29 participants in the tactile placebo group (79%) but only 14 out of 30 participants (47%) in the non-tactile placebo group believed that they had received the active intervention (p = 0.015). Bang’s blinding index (BI) indicated random guessing in the non-tactile placebo group (BI = 0; 95% CI, −0.35 to 0.35) and non-random guessing in the direction of an “opposite guess” in the tactile placebo group (BI = −0.52; 95% CI, −0.81 to −0.22).ConclusionTactile stimulation during placebo TENS did not further enhance positive treatment expectations and the placebo effect in nausea but increased the credibility of the intervention. Further trials should investigate the interaction between perceived treatment assignment, expectation, and the placebo effect during the course of a trial.
Highlights
Tactile stimulation during a placebo treatment could enhance its credibility and thereby boost positive treatment expectations and the placebo effect
The small specific effect of acupuncture compared to the large overall effect indicates the involvement of “nonspecific” factors, such as expectation and tactile stimulation, which contribute to the success of acupuncture treatment
We recently showed that a placebo transcutaneous electrical nerve stimulation (TENS) stimulation at a dummy point, which elicited slight tactile stimulation, induced a large placebo effect on experimentally induced nausea in comparison to a no-treatment control condition in female participants (Müller et al, 2016)
Summary
Tactile stimulation during a placebo treatment could enhance its credibility and thereby boost positive treatment expectations and the placebo effect. The overall improvement after acupuncture is usually large (Linde et al, 2010a,b; Meissner et al, 2013). The small specific effect of acupuncture compared to the large overall effect indicates the involvement of “nonspecific” factors, such as expectation and tactile stimulation, which contribute to the success of acupuncture treatment. In four large RCT of acupuncture, for example, patients with chronic pain conditions and high outcome expectations at baseline showed larger pain reduction at follow-up regardless of whether they were allocated to active acupuncture or placebo acupuncture (Linde et al, 2007). The non-verbal cues of a treatment, such as prizing, labeling, and dosing, can increase outcome expectations and the placebo effect (Meissner and Linde, 2018). Placebo effects have been demonstrated for various clinical conditions including nausea (Quinn and Colagiuri, 2014, 2016; Müller et al, 2016), depression and anxiety (Meyer et al, 2015; Peciña et al, 2015; Rutherford et al, 2016), Parkinson’s disease (De la Fuente-Fernández et al, 2001; Benedetti et al, 2004; Lidstone et al, 2010), as well as for gastrointestinal and cardiovascular systems (Meissner, 2009, 2011; Meissner and Ziep, 2011; Meissner et al, 2011; Ronel et al, 2011; Meissner, 2014; Rief et al, 2017) and immune responses (Hadamitzky et al, 2018)
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