Initially, 12 volunteers at the Technical University of Aachen had a heating device placed on their skin to determine the temperature that each volunteer considered painful (8 out of 10 on a 0 to 10 pain scale). The volunteers were then split into two groups. One group was hypnotized, placed in the fMRI machine and their brain activity scanned while the painful thermal stimuli was applied. Then the hypnotic state was broken and a second fMRI scan was performed without hypnosis while the same painful heat was again applied to the volunteer's skin. The second group underwent their first fMRI scan without hypnosis followed by a second scan under hypnosis.
Hypnosis was successful in reducing pain perception for all 12 participants. Hypnotized volunteers reported either no pain or significantly reduced pain (less than 3 on the 0-10 pain scale) in response to the painful heat.
Under hypnosis, fMRI showed that brain activity was reduced in areas of the pain network, including the primary sensory cortex, which is responsible for pain perception.
The imaging studies also showed increased activation in two other brain structures - the left anterior cingulate cortex and the basal ganglia. The researchers speculate that increased activity in these two regions may be part of an inhibition pathway that blocks the pain signal from reaching the higher cortical structures responsible for pain perception. However, Schulz-Stubner noted that more detailed fMRI images are needed to definitively identify the exact areas involved in hypnosis-induced pain reduction, and he hoped that the newer generation of fMRI machines would be capable of providing more answers.