Journal of behavioral medicine
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Randomized Controlled Trial
Expectations and placebo response: a laboratory investigation into the role of somatic focus.
It has been theorized that expectations are an important causal determinant of the placebo effect. Placebo expectations, however, do not always yield placebo effects. In a laboratory study, we tested the hypothesis that one's level of somatic focus moderates the effect of placebo expectations on placebo responding. ⋯ The results revealed that individuals who thought they were taking a drug (i.e., unconditional expectations) reported more placebo symptoms when they closely focused on their symptoms. Individuals told they may or may not be receiving a drug (i.e., conditional expectations) did not differ from control participants regardless of how closely they attended to their symptoms. The findings have theoretical implications for expectancy models of the placebo effect as well as for practical research comparing the type of expectations held by individuals in clinical trials and clinical practice.
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Despite relatively standardized surgical procedures, patients undergoing total knee replacement (TKR) surgery differ dramatically in the speed of their recovery. Previous research has suggested a relationship between the experience of pain and sleep disruptions among patients with chronic pain or those undergoing surgery, such that more severe pain is associated with more frequent awakenings throughout the night. ⋯ After controlling for presurgical levels of pain, sleep disruptions, and functional limitations, sleep disruptions 1 month following surgery partially mediated the relationship between pain 1 month following surgery and functional limitations 3 months following surgery. The present findings underscore the importance of adequate sleep during postsurgical recovery and suggest that interventions targeting sleep disruptions may improve the speed and quality of patients' recovery from TKR and other surgical procedures.
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Greater trait anger-out is associated with elevated pain responsiveness. Previous work suggests this effect may be mediated by deficient endogenous opioid analgesia, possibly reflecting diminished opioid receptor sensitivity. The A118G single nucleotide polymorphism (SNP) of the mu opioid receptor gene influences both opioid receptor sensitivity and clinical responsiveness to opioid analgesics. ⋯ Anger-out was not associated with A118G SNP status (p > 0.10), suggesting the latter is unlikely to mediate anger-out's pain-related effects. A significant anger-out x A118G interaction was observed on analgesic use (p < 0.05), due to a much stronger positive relationship between anger-out and analgesic demands in patient with the A118G SNP (b = 0.53) than those with the wild-type receptor (b = 0.07). These results suggest that the A118G SNP may moderate but not mediate the effects of anger-out on postoperative pain responses.