updated 12/21/2005 11:27:05 AM ET 2005-12-21T16:27:05

Researchers at the University of Michigan have found a "pleasure spot" in the brains of rats that may shed light on how food translates into pleasure for humans.

The spot in rats' brains makes sweet tastes more "liked" than other tastes, biopsychology researchers Susana Pecina and Kent Berridge found. The pair detailed their findings in the Dec. 14 issue of the Journal of Neuroscience.

Sweetness by itself is merely a sensation, they note. Its pleasure arises within the brain, where neural systems actively paint pleasure onto the sensation to generate a "liking" reaction.

The study pinpointed a pleasure spot within a larger part of the brain responsible for appetite in the nucleus accumbens, the lower front of the brain.

"There's a 'liking' cube tucked within a larger 'wanting' cube," Berridge said in a telephone interview.

Previously, scientists knew the general part of the brain that was responsible for pleasure and appetite. But they did not know whether those functions were separable, Berridge said.

"In our experience, they're intertwined and inseparable," Berridge said. "In our brain, they are separable."

Pecina and Berridge made microinjections into rats' brains of drugs that stimulated receptors for opioids, or heroinlike substances, causing nearby neurons to activate particular genes that began producing proteins.

The microinjections caused rats to eat more food soon afterward. Using a new mapping technique, the researchers pinpointed where in the brain the microinjections activated increased liking reactions. The pleasure spot was much smaller than the larger appetite-increasing zone.

Berridge said the study could ultimately have applications for treating eating disorders.

The researchers used sweet things in their study, but Berridge noted the reaction would be the same with any liked food.

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