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Brain imaging studies investigate pain reduction by hypnosis
Although
hypnosis has been shown to reduce pain perception, it is not clear how
the technique works. Identifying a sound, scientific explanation for
hypnosis' effect might increase acceptance and use of this safe
pain-reduction option in clinical settings.
Researchers at the University of Iowa Roy J. and Lucille
A. Carver College of Medicine and the Technical University of Aachen,
Germany, used functional magnetic resonance imaging (fMRI) to find out
if hypnosis alters brain activity in a way that might explain pain
reduction. The results are reported in the November-December 2004
issue of Regional Anesthesia and Pain Medicine.
The researchers found that volunteers under hypnosis
experienced significant pain reduction in response to painful heat.
They also had a distinctly different pattern of brain activity
compared to when they were not hypnotized and experienced the painful
heat. The changes in brain activity suggest that hypnosis somehow
blocks the pain signal from getting to the parts of the brain that
perceive pain.
"The major finding from our study, which used fMRI for
the first time to investigate brain activity under hypnosis for pain
suppression, is that we see reduced activity in areas of the pain
network and increased activity in other areas of the brain under
hypnosis," said Sebastian Schulz-Stubner, M.D., Ph.D., UI assistant
professor (clinical) of anesthesia and first author of the study. "The
increased activity might be specific for hypnosis or might be
non-specific, but it definitely does something to reduce the pain
signal input into the cortical structure."
The pain network functions like a relay system with an
input pain signal from a peripheral nerve going to the spinal cord
where the information is processed and passed on to the brain stem.
From there the signal goes to the mid-brain region and finally into
the cortical brain region that deals with conscious perception of
external stimuli like pain.
Processing of the pain signal through the lower parts of
the pain network looked the same in the brain images for both
hypnotized and non-hypnotized trials, but activity in the top level of
the network, which would be responsible for "feeling" the pain, was
reduced under hypnosis.
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.
"Imaging studies like this one improve our understanding
of what might be going on and help researchers ask even more specific
questions aimed at identifying the underlying mechanism," Schulz-Stubner
said. "It is one piece of the puzzle that moves us a little closer to
a final answer for how hypnosis really works.
"More practically, for clinical use, it helps to dispel
prejudice about hypnosis as a technique to manage pain because we can
show an objective, measurable change in brain activity linked to a
reduced perception of pain," he added.
In addition to Schulz-Stubner, the research team
included Timo Krings, M.D., Ingo Meister, M.D., Stefen Rex, M.D.,
Armin Thron, M.D., Ph.D. and Rolf Rossaint, M.D., Ph.D., from the
Technical University of Aachen, Germany.
University of Iowa Health Care describes the partnership
between the UI Roy J. and Lucille A. Carver College of Medicine and UI
Hospitals and Clinics and the patient care, medical education and
research programs and services they provide. Visit UI Health Care
online at uihealthcare.com.
STORY SOURCE: University of Iowa Health Science
Relations, 5135 Westlawn, Iowa City, Iowa 52242-1178
MEDIA CONTACT: Jennifer Brown, (319) 335-9917,
jennifer-l-brown@uiowa.edu
Contact: Jennifer Brown
jennifer-l-brown@uiowa.edu
319-335-9917
University of Iowa
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