The Journal of neuroscience : the official journal of the Society for Neuroscience
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Randomized Controlled Trial Clinical Trial
Conscious expectation and unconscious conditioning in analgesic, motor, and hormonal placebo/nocebo responses.
The placebo and nocebo effect is believed to be mediated by both cognitive and conditioning mechanisms, although little is known about their role in different circumstances. In this study, we first analyzed the effects of opposing verbal suggestions on experimental ischemic arm pain in healthy volunteers and on motor performance in Parkinsonian patients and found that verbally induced expectations of analgesia/hyperalgesia and motor improvement/worsening antagonized completely the effects of a conditioning procedure. ⋯ These findings indicate that verbally induced expectations have no effect on hormonal secretion, whereas they affect pain and motor performance. This suggests that placebo responses are mediated by conditioning when unconscious physiological functions such as hormonal secretion are involved, whereas they are mediated by expectation when conscious physiological processes such as pain and motor performance come into play, even though a conditioning procedure is performed.