Pain researchers say they may have discovered one of the ways in which the placebo effect works.
The authors of a new study believe their findings could have implications for future treatments of chronic pain.
The German team used heat to apply pain to volunteers' arms, telling some they had been given a painkilling cream which was, in fact, inert.
In a short article published in Science, Falk Eippert and colleagues from the University Medical Centre, Hamburg, found those who believed they had received pain relief experienced a dampening of the pain signalling in a region of the spinal cord called the dorsal horn.
The authors said: "In line with behavioural data that show decreased pain responses under placebo, pain-related activity in the spinal cord is strongly reduced under placebo.
"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 team said their work was clinically significant because it "opens up new avenues for assessing the efficacy and possible site of action of new treatments for various forms of pain, including chronic pain".