ABSTRACT
Since the rst medical practices and healing rituals were performed in ancient civilizations, the ability of the mind to inŸuence the healing of the body has been recognized across many cultures. Modern medical research has termed this the placebo effect, which is essentially the patient’s ability to demonstrate improvement in his or her condition in response to some type of “inert” treatment-whether it be a pill, an injection, or even sham surgery-but not from any properties that the treatment itself possesses. In 1811, Hooper’s Medical Dictionary dened a placebo as “an epithet given to any medicine adapted more to please than to benet the patient” [1]. Ironically, scientic investigation, in the realization of this phenomenon, needed to account for the placebo effect in the interpretation of experimental results, and, thus, the placebo effect was largely considered to be a nuisance obscuring the true effects of the active treatment. However, with the growing amount of research available from clinical drug trials, the ability of placebos to produce therapeutic benet in patients who suffer from various neurological disorders has proven to be real and effective. It has also been suggested that a placebo analgesic effect beyond the natural evolution of disease is detectable over time [2] and that this placebo effect can be augmented with an optimal patient-practitioner relationship [3]. It is now accepted that a prominent placebo effect may occur in the setting of experimental and clinical pain, depression, and Parkinson’s disease (PD) [4-6]. In the case of the latter, several randomized, placebo-controlled trials aimed at testing new pharmaceutical therapies have shown objective improvements in motor performance following placebo administration [7]. However, the precise neuropsychological and biochemical mechanisms underlying the placebo effect are only beginning to be unraveled. The original observation by Levine et al. in the late 1970s
that placebo analgesia can be blocked by naloxone suggested that the placebo effect in pain disorders involves the release of endogenous opioids [8]. Following recent studies revealing direct biochemical evidence that a patient’s expectation is central to the placebo response in PD [9], research is currently directed at characterizing the psychological and biochemical links between the expectation of benet and the improvement of motor function in patients. This “expectation theory” of the placebo effect is thought to depend upon reward circuitry in the brain and, more specically, as recent evidence suggests, to dopamine release in the ventral striatum. Theories aside, it is clear that placebos can modify not only the patient’s beliefs as to how he or she feels, but they can also have measurable effects on supposedly objective measures made by blinded evaluators [10,11].
