Researchers in Germany found that when they treated volunteers with a placebo that they believed to be a painkiller, scans showed reduced signs of pain-related activity in their spinal cords.
The study is the work of Dr Falk Eippert and colleagues, from the University Medical Center Hamburg-Eppendorf, one of the largest hospitals in Hamburg, and is published online in the 16 October issue of Science.
A placebo is an inactive substance that researchers use in “blind” trials. One group of participants receives the active drug, for example a painkiller, while another group receives the placebo, an inactive substance, but neither group knows who has received which drug.
Studies show that sometimes the participants who receive the inactive drug or placebo experience a measurable degree of pain relief, even though they are not “supposed to”.
In the background information of the study, Eippert and colleagues wrote that placebo analgesia or pain-relief is a “prime example of the impact that psychological factors have on pain perception”.
For the study they enrolled 15 healthy young male volunteers and measured their pain threshold by applying heat to their arms.
Then, like a blind trial, they told the volunteers they were applying two creams to their arms: one was a highly effective painkiller and the other one was an inactive cream that would have no effect. In fact both creams were inactive, ie both were placebos, but the researchers didn’t tell them this.
The researchers then applied heat to the treated parts of the participants’ arms (one part had been treated with what they believed was the effective painkiller and the other part treated with what they believed was the inactive cream).
The participants reported experiencing less pain in the areas that had been treated with what they believed was the effective painkiller.
During the trial the researchers also scanned the participants’ spinal cords using functional magnetic resonance imaging (fMRI), and found that when the participants were treated with what they believed was the effective painkiller, the dorsal horn of their spinal cords, where pain is processed, showed less activity compared to when they were treated with what they believed, and indeed was, an inactive cream.
Eippert and colleagues wrote that:
“These results provide direct evidence for spinal inhibition as one mechanism of placebo analgesia and highlight that psychological factors can act on the earliest stages of pain processing in the central nervous system.”
They said they hope this finding will help develop new ways of using drugs for pain relief.
“Direct Evidence for Spinal Cord Involvement in Placebo Analgesia.”
Falk Eippert, Jürgen Finsterbusch, Ulrike Bingel, Christian Büchel.
Science, 2009, Vol. 326. no. 5951, p. 404.
Published online 16 October 2009
Written by: Catharine Paddock, PhD