Placebos: Is It All in Your Spine?

Researchers have found evidence that the placebo effect is not all “in your mind.” This study, recently published in Science, suggests that the spinal column—specifically, the dorsal horn—may be involved in blocking pain after placebo has been administered. Eippert and colleagues¹ examined pain reactions in 13 young, healthy men (21 to 30 years old) after applying 2 types of cream on their forearms. The participants were told that one cream was a highly effective analgesic (“lidocaine”) and the other was a control cream. In reality, both creams were identical and pharmacologically inactive; the one labeled lidocaine was used to measure the placebo response.

Participants received a series of painful heat stimulations in the areas where the creams were applied and then were asked to rate pain levels from 1 to 100 for both the “lidocaine” (ie, placebo) and control cream areas. Significantly less pain was reported for the placebo area (mean=52.3±5.9) than the control area (mean=71.1±3.1; p=0.002).

Next, the researchers assessed spinal cord blood oxygen level-dependent responses for the placebo and control creams via high resolution functional MRIs. Two sessions of 15 pain stimulation trials were completed, one session for placebo and one for control. Functional images of the spinal column were taken of spinal segments C5 to T1.

The researchers found a distinct cluster in the ipsilateral dorsal horn, which suggested an increased neural response to pain. The cluster was not apparent in the placebo images. The researchers thus concluded that the participants’ belief in the placebo resulted in the inhibition of spinal cord nociceptive processing at the earliest stage of the CNS.

Not only does this research shed new light on the mysterious mechanisms of the placebo effect, it lays the foundation for possible pain management breakthroughs. Eippert and colleagues noted: “The demonstration that modulatory influences on nociceptive spinal cord activity are measurable by fMRI in humans opens up new avenues for assessing the efficacy and possible site of action of new treatments for various forms of pain, including chronic pain.”