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Feeling Fat (or Thin) May Be a Trick of the Mind
Whether you feel fat, thin or something in between
has little to do with the reality of the situation, suggests
a new study led by the University College London (UCL) and
published in the journal Public Library of Science Biology.
A person's self-image is an illusion constructed in the brain,
the researchers say.
Dr. Henrik Ehrsson of the UCL Institute of Neurology
and colleagues used a trick called "the Pinocchio illusion"
to give study volunteers the sensation that their waists were
shrinking. They used functional magnetic resonance imaging
(fMRI) to scan the participants' brains during the experience
and observe which parts of the brain are involved in body
image.
The results may shed some light on anorexia,
an eating disorder, and body dysmorphic disorder. People with
the latter condition typically are overconcerned about a small
or imagined defect in their body, and they frequently overestimate
or underestimate their actual body size.
Brain Creates a Map of the Body
A vibrating device placed on each study volunteer's
wrist served to stimulate the tendon and create the sensation
that the joint was flexing, even though it remained stationary.
When their hands touched their waists, the volunteers felt
their wrists bending, creating the illusion that their waists
were shrinking.
During the tendon exercise, all 17 participants
felt that their waist had shrunk by up to 28 percent. The
researchers found high levels of activity in the posterior
parietal cortex, an area of the brain that integrates sensory
information from different parts of the body. Volunteers who
reported the strongest shrinking sensation also showed the
strongest activity in this area of the brain.
"We process information about our body size
every day, such as feeling thin or fat when we put our clothes
on in the morning, or when walking through a narrow doorway
or ducking under a low ceiling," says Dr. Ehrsson.
"However -- unlike more elementary bodily senses
such as limb movement, touch and pain -- there are no specialized
receptors in the body that send information to the brain about
the size and shape of body parts. Instead, the brain appears
to create a map of the body by integrating signals from the
relevant body parts, such as skin, joints and muscles, along
with visual cues," Dr. Ehrsson adds.
Alice in Wonderland Syndrome
"Other studies have shown that people with injuries
in the parietal cortex area of the brain experience the feeling
that the size and shape of their body parts have changed.
People who suffer from migraine with aura can sometimes experience
a phenomenon called the 'Alice in Wonderland syndrome,' where
they feel that various body parts are shrinking," notes. Dr.
Ehrsson.
"This could also be linked to the same region
of the brain," he points out.
"In addition, people with anorexia and body
dysmorphic disorder who have problems with judging the size
of their body might similarily have a distorted representation
of their body image in the parietal cortex. These are areas
which would be worth exploring in future research, to establish
whether this region of the brain is involved in anorexia and
the rare but peculiar shrinking symptoms of some migraines,"
Dr. Ehrsson concludes.
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About the Author:
Rita Jenkins is a health journalist for Daily News Central,
an online publication that delivers breaking news and reliable
health information to consumers, healthcare providers and
industry professionals: http://www.dailynewscentral.com
Copyright 2005 Daily News Central
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