When you’ve eaten a good meal at a restaurant and the waiter asks, “Got any room for dessert?” where does the voice that craves a gratuitous slice of pie come from?

Your brain.

Scientists now have a better understanding of the neural origins of this urge thanks to a new study published in the journal Science last week.

Mice brains are structurally similar to human brains. So, to isolate the neural pathways responsible for “dessert brain,” the researchers turned to mice.

Researchers at the Max Planck Institute for Metabolism Research fed mice to the point of fullness and then gave them sugar. In doing so, they found that the same neurons signaling satiety, or fullness, also released β-Endorphin, a naturally-occurring opiate. This chemical bound to opiate receptors in the mice brains and triggered a feeling of reward. When the team then blocked this opiate pathway, the mice stayed away from the sugar.

The researchers found the same neural mechanism in humans when studying donated brain tissue and scanning the brains of volunteers.

Henning Fenselau, one of the study authors, says this suggests that people’s brains evolved to love sugar in excess. “Because sugar is so easy to metabolize, its consumption beyond energy needs is favorable for animals,” he says.

Ultimately, the team hopes this research can lead to a better understanding of sugar overconsumption, obesity and more sophisticated weight-loss drugs.

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This episode was produced by Hannah Chinn, Berly McCoy and Alejandra Marquez Janse. It was edited by Rebecca Ramirez and Christopher Intagliata. Tyler Jones checked the facts. Becky Brown and Jimmy Keeley were the audio engineers.