Washington - 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 on Monday.

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."