The placebo effect can be traced in part to physical changes that take place in the spine when a fake drug is taken, according to a study conducted by researchers from the University Medical Center Hamburg-Eppendorf in Germany, and published in the journal Science.

The placebo effect refers to a phenomenon in which a person's symptoms diminish after taking a biologically inactive treatment that they believe to be a real drug. It is a well-documented effect that is particularly strong for conditions originating in the central nervous system, such as pain and depression.

"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," the researchers wrote.

Researchers told 15 healthy men that their arms were being treated with two separate creams - one of them an anesthetic, the other a placebo. They then applied painful heat to the treated sections of the participants arms while taking a functional magnetic resonance imaging (fMRI) scan of their spinal cords.

Both creams were, in fact, medically inactive placebos. Yet the men not only reported experiencing significantly less pain when treated with a cream they believed to be active, but the fMRI scans showed that the activity of the nerves in their spine was also significantly reduced. This shows that when given a placebo, the mind is not just filtering pain away - the body actually feels less.

"It is deeply rooted in very, very early areas of the central nervous system. That definitely speaks for a strong effect," lead researcher Falk Eippert said.

The researchers still could not explain how the perception of treatment created an effect in the spine, however. They suggested that the body might respond to treatment with a perceived drug by releasing its own natural painkillers.