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Pain Reduction by Hypnosis:
Brain Imaging Studies
You
might have heard that hypnosis can provide comfortable birth to
women and ease pain in burn victims. But do you know how hypnosis
reduces pain?
Researchers
at University of Iowa and the Technical University of Aachen, Germany
used functional magnetic resonance imaging (fMRI) and found that
hypnosis alters brain activity in a way that might explain pain
reduction by hypnosis.
The
researchers found that volunteers under hypnosis experienced significant
pain reduction in response to painful heat. They also had a distinctly
altered pattern of brain activity compared to when they experienced
the painful heat while not in hypnosis. The brain activity imaging
suggests that hypnosis somehow blocks the pain signal from reaching
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
Experiment
1.
Twelve 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).
2.
The volunteers were then split into two groups.
Group #1: The fMRI twice scanned their brain activity while the
same painful heat was applied, first under hypnosis, then out of
hypnosis.
Group #2: The fMTI scan was used first without hypnosis, then under
hypnosis.
Pain
Reduction Results
1.
Perception of Pain
Hypnosis
was successful in reducing self-reported 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.
2.
Brain Activity Under Hypnosis as Shown in fMRI Scan
As
explained in the University of Iowa news release, 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." The fMRI imaging in this study showed:
- 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.
- Under
hypnosis, brain activity was reduced in areas of the pain network,
including the primary sensory cortex, which is responsible for
pain perception.
- Under
hypnosis, brain activity was increased in the left anterior cingulate
cortex and the basal ganglia, which lead to the speculation these
two regions may be part of an inhibition pathway that blocks the
pain signal from reaching the higher cortical structures.
More
detailed brain activity images generated by more advanced fMTI machines
are needed to definitively identify the exact areas involved in
hypnosis-induced pain reduction.
"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.
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