Eating when you're not hungry -- especially high-calorie, high-fat foods -- may not always rise to the newly broadened clinical definition of an eating disorder. But the behavior that for many Americans is a routine pastime certainly contributes to excess weight gain, with its implications for health. And it is considered "disordered eating" by most mental health professionals.

A study published Thursday in the journal Science adds to evidence that binge eating -- and overeating generally -- may have a biological basis. The new research, conducted on mice, suggests a target in the brain that drug developers should consider in exploring treatments for such disordered eating.

Not surprisingly, researchers focused their attention on the hypothalamus, one of the brain's most primitive structures, a key node in the brain circuitry that drives us to eat and drink, to seek out sexual partners, and generally to crave more of what makes us feel good.

To explore how the lateral hypothalamus governs eating behavior, researchers from the University of North Carolina used mice and a relatively new technique: To discern how certain cells work, they genetically engineered the cells to respond to light; then, they turned those cells on and off, essentially, with a miniature flashlight, and watched the resulting behavior.

When they "turned on" these unique cells in mice who were well fed, the result was rapid and striking: The animals immediately launched into "voracious feeding behavior." And the mice clearly enjoyed the impulse to pig out: They showed a clear preference for being in the space they associated with having the cells turned on.

Moreover, given the choice, the animals made a beeline to high-fat, high-calorie foods.

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