Further evidence for individual differences in placebo responding: an interactionist perspective.
ABSTRACT A prior investigation found that individuals low in optimism are more likely to follow a negative placebo (nocebo) expectation. The present study tested the hypothesis that individuals high in optimism are more likely to follow a positive placebo expectation.
Individuals (N=56) varying in their level of optimism were randomly assigned to one of three conditions. In the first condition, participants were given the expectation that a placebo sleep treatment would improve their sleep quality (placebo expectation condition). In the second condition, participants engaged in the same sleep treatment activity but were not given the positive placebo expectation (treatment control condition). Finally, a third group did not receive the positive placebo expectation and also did not engage in the placebo sleep treatment (no-placebo control condition).
Optimism was positively associated with better sleep quality in the placebo expectation condition (r=.48, P<.05). Optimism scores were not associated with better sleep quality in either the treatment control condition (r=-.17, P=.46) or the no-placebo control condition (r=-.24, P=.35).
Dispositional optimism relates to placebo responding. This relationship, however, is not manifested in a simple increase or decrease in all types of placebo responding. Rather, it appears that, as optimism increases, response to the positive placebo expectation increases, whereas response to nocebo expectation decreases. It is recommended that future research on personality and placebo effects consider the interaction between situational and dispositional variables.
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ABSTRACT: New high-voltage power transmission lines will be introduced due to increasing demand for reliable and renewable energy supplies. Some residents associate non-specific health complaints with exposure to electromagnetic fields from nearby power lines. This study protocol describes the design and rationale of a prospective study investigating whether the introduction of a new power line triggers health responses in residents living nearby. Methods/design: The study is designed as a quasi-experimental field study with two pretests during the construction of a new power line route, and two posttests after it has been put into operation. Key outcomes are self-reported non-specific somatic and cognitive health complaints, and attribution of these health complaints to a power line. The main determinant is proximity to the new power line route. One member of every household (N = 2379) residing in close proximity (0-500 meters) to the overhead parts of a new power line route in the Netherlands is invited to participate, as well as a sample of household members (N = 2382) residing farther away (500-2000 meters). Multilevel analysis will be employed to test whether an increase in key outcome measures is related to proximity to the line. Longitudinal structural equation models will be applied to test to what extent health responses are mediated by psychosocial health mechanisms and moderated by negative oriented personality traits. This is the first study to investigate health responses to a new power line route in a prospective manner. The results will provide theoretical insight into psychosocial mechanisms operating during the introduction of an environmental health risk, and may offer suggestions to policymakers and other stakeholders for minimizing adverse health responses when introducing new high-voltage power lines.BMC Public Health 03/2014; 14(1):237. · 2.08 Impact Factor
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ABSTRACT: Aim: To identify personality traits related to placebo responding outside the context of pain. Methods. Sixty three healthy volunteers completed the study. Personality traits were measured online one week prior to a laboratory session in which two psychosocial stress tests were administered. Prior to the second test, the placebo group received an intranasal spray of ‘serotonin’ (placebo) with the suggestion it would enhance recovery. Subjective stress, heart rate and heart rate variability were measured. Self reported and physiological responses to the placebo suggestion were assessed against personality variables. Results. Placebo effects were demonstrated in both self reported and physiological stress metrics. Lower optimism and less empathic concern predicted greater perceived benefits from the placebo treatment; and lower drive, fun, and sensation seeking were related to a greater physiological response to the manipulation. Multivariate analyses revealed lower optimism and behavioural drive to be predictive of responding to the placebo manipulation. Conclusion. Findings are in contrast with prior work in pain paradigms which found higher levels of the same traits to be related to greater placebo analgesic responses. A cluster of traits characterised by behavioural drive, extraversion, optimism and novelty or fun seeking appears to be germane to placebo responsiveness, but contextual stimuli may generate different patterns of responding. A new conceptualisation of placebo responsiveness may be useful. Rather than a ‘placebo personality’ it may be that responsiveness is better typified by a two faceted transactional model, in which different personality facets respond to different contextual contingencies.Journal of Psychosomatic Research 04/2014; 76(5). · 3.27 Impact Factor
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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.PLoS ONE 01/2014; 9(3):e91727. · 3.73 Impact Factor