Role of Conditioning and Verbal Suggestion in Placebo and Nocebo Effects on Itch

Abstract

Placebo and nocebo effects are known to play a key role in treatment effects in a wide variety of conditions. These effects have frequently been investigated with regard to pain and also in other physical sensations, but have hardly been investigated with regard to itch. In addition, neither in pain nor in any other physical sensation, the single and combined contribution of the expectancy mechanisms of conditioning and verbal suggestion have ever been investigated in both placebo and nocebo effects within one design. For the first time, the role of verbal suggestion and conditioning in placebo and nocebo effects on itch was experimentally investigated. Expectations about itch stimuli were induced in healthy subjects by verbal suggestion, conditioning, or a combination of both procedures, and compared with a control group without expectation induction. Itch was induced electrically by means of quantitative sensory testing. Significant placebo and nocebo effects were induced in the group in which combined procedures of conditioning and verbal suggestion were applied in comparison with the control group. The conditioning and verbal suggestion procedures applied individually did not induce significant placebo and nocebo effects when compared with the control group. The results of this study extend existing evidence on different physical sensations, like pain, by showing that also for itch, the combination of conditioning and verbal suggestion is most promising in inducing both placebo and nocebo effects. More research on placebo and nocebo effects at a perceptive and neurobiological level is warranted to further elucidate the common and specific mechanisms underlying placebo and nocebo effects on itch and other physical sensations.

Relieving patients' pain with expectation interventions

“…This finding is in contrast with previous research in healthy samples, where such procedures are generally observed to have more robust effects on pain than verbal suggestions alone. 6,47,54 However, because the effects of conditioning in clinical samples could be analyzed only in 3 studies and were studied only on experimental pain, and because conditioning procedures were always paired with verbal suggestion, no firm conclusions can be drawn yet about the size of conditioning effects in clinical samples. Imagery was found to have a small effect on clinical pain in our meta-analysis.…”

“…For example, pairing a placebo treatment with reduced pain stimulation can produce expected and experienced pain relief when merely receiving the placebo treatment, 1,15,45,46,59,78 especially when conditioning is paired with a verbal suggestion. 6,46,52 Mental imagery of a future event or desired outcome entails actively generating a multisensory cognitive representation of an event and often involves relatively implicit suggestions. 28,35 For example, imagining an optimal future self or health can increase general positive expectations (ie, optimism) 56,60,61 and correspondingly reduce pain and medical care utilization.…”

Nocebo effect in Dermatology

“…[46] In a recent study by Bartels et al, who investigated the role of verbal suggestion and conditioning in placebo and nocebo effects on itch, the subjects receiving both conditioning and verbal suggestion experienced significant nocebo effects, that is, subjects experienced a lot more itch when they were verbally suggested and conditioned with visual cues that the stimulus would evoke more itch than when given neutral suggestions (control group). [12] Another interesting finding of this study was the statistically significant association of nocebo effect with individual psychological characteristics of hope, extraversion, negative affect, and worrying. Greater nocebo responses were observed with more worry and negative effect, less hope, and lower levels of extraversion.…”

“…[9] Their effects in non-pain-related conditions have been explored only recently. [10][11][12] Nocebo response requires the interaction of a stimulus with conscious or subconscious expectation of a negative response, which may occur at cortical, subcortical, and/or spinal level. [9,13,14] For example, when an inert cream suggested to contain capsaicin was applied over the forearm of a human volunteer, evaluation by functional magnetic resonance imaging revealed lowered pain threshold and increased pain perception.…”

The Placebo Phenomenon: A Narrow Focus on Psychological Models

“…Moreover, some learning processes may occur independently of conditioning by means of vicarious observation, social learning, or verbal communication (Kirsch 1985, 1997, 2004). Given that placebo effects have been demonstrated to be influenced by verbal suggestions, conditioning processes, social observation, personality factors, and genetics, the underlying endogenous mechanisms mediating the processing of the vast amount of information within a clinical environment are far more integrated and complex than one single process alone (Bartels et al 2014; Benedetti et al 2003; Brody and Brody 2000; Colagiuri et al 2015; Colloca and Benedetti 2006, 2009; Colloca and Grillon 2014; Corsi and Colloca 2017; Darragh et al 2015; Hall, Loscalzo, and Kaptchuk 2015; Kirsch 2004; Klinger et al 2017b; van Laarhoven et al 2011; Vase et al 2003; Vogtle, Barke, and Kroner-Herwig 2013; Wang et al. 2017).…”