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The Placebo Effect: A very basic neurological process

Posted by admin at 8:07 PM Tuesday, March 30, 2010


The placebo effect – the curious phenomenon in which a patient feels better and even gets better when he thinks he is receiving treatment but in fact is not – has received great attention by the scientific and medical communities and by the general public in the recent decades. After its discovery, experimental medical trials had to be redesigned to account for it, and a race began among scientists to elucidate how this extraordinary “treatment” works. Many of the following studies have focused on the placebo effect of relieving pain (1) and considerable data now indicates that this occurs through the endogenous opioid system (the same neurological circuit activated by painkillers such as morphine) (2,3).

In this month’s edition of Neuron, Eippert et al. (4) produce solid data supporting a role of the opioid system in the placebo effect. They do this through an elegant study in which patients were given an inert treatment for a mild burn, and half of them were further administered naloxone, a drug that blocks the opioid circuits in the brain. The authors then employed a combination of two state-of-the-art medical imaging techniques – functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) – to visualize which areas of the brain “light up” in the presence and absence of the naloxone.

Their results are groundbreaking: not only do they show a clear correlation between administration of naloxone and the decrease in placebo pain relief, but they identify some very “primitive” brain components – the amygdala, the hypothalamus and part of the brainstem – as part in the placebo effect circuitry. This comes as a great surprise: because the phenomenon is the result of voluntary expectation (the patient thinks he is receiving treatment) it would be more intuitive that it mainly involved the more “evolved” and human-specific parts of the cortex.

Given these new data, one cannot help wondering: if the placebo effect is so deeply rooted in one’s brain, does that mean it is somehow connected to more crucial brain functions? And when and more importantly why, did the placebo effect evolve? Like is often the case with science, this groundbreaking discovery seems to generate more questions than it answers.

- S. Andrei Anghel
[From September 7, 2009]

  • 1. V. De Pascalis, C. Chiaradia, E. Carotenuto, Pain 96, 393 (Apr, 2002).
  • 2. P. Grevert, L. H. Albert, A. Goldstein, Pain 16, 129 (Jun, 1983).
  • 3. J. D. Levine, N. C. Gordon, H. L. Fields, Lancet 2, 654 (Sep 23, 1978).
  • 4. F. Eippert et al., Neuron 63, 533 (Aug 27, 2009).

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