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The Journal of Neuroscience, January 11, 2006, 26(2):559-563; doi:10.1523/JNEUROSCI.4218-05.2006

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BRIEF COMMUNICATION
Placebo-Induced Changes in Spinal Cord Pain Processing

Dagfinn Matre,^1,2,3 Kenneth L. Casey,^2,3 and Stein Knardahl^1,4

¹Department of Physiology, National Institute of Occupational Health, N-0033 Oslo, Norway, ²Neurology Research Laboratory, Veterans Affairs Medical Center, and ³Department of Neurology, University of Michigan, Ann Arbor, Michigan 48105, and ⁴Department of Psychology, University of Oslo, N-0317 Oslo, Norway

Pain is an essential sensory modality, signaling injury or threat of injury. Pain perception depends on both biological and psychological factors. However, it is not known whether psychological factors modify spinal mechanisms or if its effect is limited to cortical processing. Here, we use a placebo analgesic model to show that psychological factors affect human spinal nociceptive processes. Mechanical hyperalgesia (hypersensitivity) after an injury is attributable to sensitized sensory neurons in the spinal cord. After a 5 min, 46°C heating of the skin, subjects developed areas of mechanical hyperalgesia. This area was smaller in a placebo condition compared with a baseline condition. This result suggests that placebo analgesia affects the spinal cord as well as supra-spinal pain mechanisms in humans and provides strong supporting evidence that placebo analgesia is not simply altered reporting behavior. Central sensitization is thought to mediate the exaggerated pain after innocuous sensory stimulation in several clinical pain conditions that follow trauma and nervous-system injury. These new data indicate that expectation about pain and analgesia is an important component of the cognitive control of central sensitization.

Key words: descending; spinal cord; pain; sensitization; nociception; inhibition

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Received Oct 4, 2005; revised November 22, 2005; accepted November 23, 2005.

This article has been cited by other articles:

				F. Benedetti, A. Pollo, and L. Colloca Opioid-Mediated Placebo Responses Boost Pain Endurance and Physical Performance: Is It Doping in Sport Competitions? J. Neurosci., October 31, 2007; 27(44): 11934 - 11939. [Abstract] [Full Text] [PDF]

				T. D. Wager, D. J. Scott, and J.-K. Zubieta Placebo effects on human {micro}-opioid activity during pain PNAS, June 26, 2007; 104(26): 11056 - 11061. [Abstract] [Full Text] [PDF]

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