The same brain circuits are involved when
obese people fill their stomachs as when drug
addicts think about drugs, a finding that
suggests overeating and addiction may be linked,
U.S. researchers reported.
The finding may help
in creating better treatments for obesity
-- a growing problem in the United States
and elsewhere.
"We wanted to know why, when people are already
full, why people are still eating a lot,"
said Dr. Gene-Jack Wang of Brookhaven National
Laboratory in Upton, New York.
"We were able to simulate the process that
takes place when the stomach is full, and
for the first time we could see the pathway
from the stomach to the brain that turns 'off'
the brain's desire to continue eating."
Wang and colleagues tested seven obese volunteers
who had been fitted with a gastric stimulator
-- a device that tricks the body into thinking
the stomach is full, a state known as satiety.
They used a positron emission tomography
or PET scan to see which parts of the brain
activated when the stimulator was activated.
They also carefully questioned their volunteers,
all of whom were very obese, about why and
when they overate.
"We thought the activated area (of the brain)
must be in the satiety center, which we learned
in medical school is supposed to be in the
hypothalamus," Wang said in a telephone interview.
But they did not see activity there.
"We saw a lot of activity in all areas of
the brain, especially in the hippocampus.
That region is related to learning, memory
and is also related to a lot of things such
as sensory and motor impulse and emotional
behavior," Wang said.
Writing in the Proceedings of the
National Academy of Sciences, Wang
and colleagues said the hippocampus was 18
percent more active when the gastric stimulator
was on.
The stimulators also sent messages of satiety
to brain circuits in the orbitofrontal cortex
and striatum, which have been linked to craving
and desire in cocaine addicts.
"This provides further evidence of the connection
between the hippocampus, the emotions, and
the desire to eat, and gives us new insight
into the mechanisms by which obese people
use food to soothe their emotions," said Wang.
The volunteers were all genuinely hungry
-- they had been fasting for 16 or 17 hours
when the PET scans were run. The stimulator
succeeded in making them feel less hungry,
Wang said.
But the surprise was in which brain circuits
it used in doing so.
"It was very similar to a study on when cocaine
abusers, when they think of cocaine, they
have a craving for cocaine," he said.
"This new pathway should be explored in further
studies to determine if there are any implications
for treating or preventing obesity."
