By Thomas S. May
RHODES, GREECE -- June 19, 2007 -- Hypnosis can result in a significant reduction in pain awareness, and the neurophysiological correlates of this analgesic effect have now been identified by a functional magnetic resonance imaging (fMRI) study that was presented here at the 17th Meeting of the European Neurological Society (ENS).
The study used 13 healthy subjects and tested them twice: once under hypnosis and once in a normal state. During each session, 200 laser stimuli with intensity ranging from 300 to 600 mJ were administered on the left hand. Subjects rated their sensations from P0 to P4 (P0: nothing perceived, P1: non-painful sensation, P2: mild pain, P3: moderate pain, P4: intense pain). The researchers used fMRI scans taken during the two sessions to assess activation levels in various brain regions in response to the stimulation.
The investigators found that there was a significant difference in the perception of higher intensity pain stimuli in the normal versus the hypnotic state (mean score 1.9±0.3 vs. 1.2±0.4, respectively), but not for the non-painful range of intensity (mean score 0.5±0.2 vs. 0.4±0.3, respectively).
These results show that hypnosis is most effective at altering the perception of acute pain, the researchers concluded. "Perception of intense pain was significantly altered while participants were under hypnosis," said Steven Laureys, MD, PhD, director, Coma Science Group, University of Liege, Liege, Belgium. "However, for levels of pain at the low end of the scale, hypnosis barely altered perception of the stimuli," Dr. Laureys stated.
In the normal state, high-intensity (painful) compared to low-intensity (non-painful) stimuli induced greater activation in the (bilateral) thalamus, primary somatosensory cortex (S1), insula, and the anterior cingulate cortex. But in the hypnotic state, high-intensity compared to low-intensity stimuli resulted in significantly greater activation in area S1 only, Dr. Laureys reported. There was no significant difference in activation levels in the bilateral thalamus, left insula and bilateral anterior cingulate cortex during high-intensity vs. low-intensity stimulation in subjects under hypnosis, he noted.
"We were able to clearly demonstrate, at the level of neural mechanisms, that hypnosis has actual effects in reducing pain perception," said Dr. Laureys. "It appears that pain continues to be registered in the primary somatosensory cortex," he explained, "but other areas of the brain involved in pain perception, such as the anterior cingulated gyrus, which allows sensory stimuli to trigger appropriate physical reactions and affect emotions, respond to painful stimuli significantly less in the hypnotic state, as compared to the normal state."
[Presentation title: fMRI Study of Hypnosis-induced Analgesia. Abstract O156]
E-Mail this DGDispatch to a colleague
