Semester 1, 2008
Conduct a literary review of the latest research and theoretical conclusions on the subject of the placebo effect. One of the earliest pieces of research into the placebo effect was conducted in the 1950’s at the University of Kansas Medical Centre. Placebo surgery or real surgery was conducted on a group of male patients with angina. Those who received placebo surgery had a 100% reduction in the incidence of angina. Those who had the actual surgery had only a 74% reduction in the incidence of angina. This trial prompted much interest in the placebo effect within the medical and scientific community (Hassed, 2003).
Joseph Arapala reports that in tests of psychoactive drugs, it is common for the placebo to be effective in 25 to 60% of cases. A study by Fisher and Greenberg reveals that in 30 – 40% of all studies in anti-depressant drugs they reviewed, the placebo was as powerful or therapeutic as the drug.(Arapala, 2000. Fisher, 2000)
A 1960’s study comparing the effects of a placebo in arthritis patients showed that patients who had previously had effective treatment of their arthritis were 48-55% more likely to have a positive response to placebo treatment than those who had ineffective past treatment (Hassed, 2003).
A meta-analysis to provide an evidence-based estimate of the magnitude of the placebo response in Restless Leg Syndrome found the pooled placebo response rate was 40.09% (95% CI: 31.99–48.19) over the eligible 24 trials sampled ( Fulda & Wetterrences, 2008).
Certainly it seems that the medical and scientific community take the placebo effect seriously. I somehow get the impression that they find it rather a nuisance. It gets in the way of serious research. Research has shown that the placebo effect is real and very powerful, often more powerful than “actual treatments”.
Wikramesekera (1999) claims the placebo effect and other non-specified factors account for 70% of the response to biofeedback. He explains this as a conditioned response based on memory of previous healings. This hypothesis goes some way to explaining why patients in the placebo arthritis study in the 1960’s had a stronger response if they’d had previous successful treatment but does not go on to describe the mechanism at work. To me this seems a fairly vague explanation that does not explain the mechanism employed by the conditioned response to enact a physical response.
Much of the research done on the mechanisms by which placebos act has centred on pain control. Six recent papers point to a major role for rostral anterior cingulate cortex (rACC) (Petrovic et al., 2002; Pariente et al., 2005; Bingel et al., 2006; deCharms et al., 2006; Kong et al., 2006; Zubieta et al., 2006) and the brainstem indicating a shared neural mechanism in pain relief (Seminowicz, 2006).
Petrovic found that the anterior cingulate cortex (ACC) and the right anterior insula (AI) were also implicated and that these changes can be mediated by several mechanisms, including altered descending modulation via brainstem inhibitory systems and activation of endogenous opioid systems. Strategically positioned to form a loop from limbic to brainstem to medial prefrontal regions, the rACC is densely populated with µ-opioid receptors and is activated by opioid as well as placebo analgesia.
The recent paper by Kong et al. (2006) reported placebo-related activation of rACC, right AI, lateral prefrontal cortex, and inferior parietal cortex. In particular, rACC and pons activity correlated with placebo response, as did several prefrontal cortical regions.
The placebo effect in Parkinson's disease has also been shown to be mediated via the release of dopamine in the dorsal striatum. Researchers claim this establishes a connection between the placebo effect and activation of the reward circuitry in the brain (De la Fuent-Fernandex, 2002).
It seems that there is general agreement from most researches that a...