Sometimes, you open a bag of chips. And sometimes, five minutes later, you reach into that same bag and come up empty. Late-night snacking can be a dietary sore point for many of us, and occasionally involves overeating.

Now, researchers from the University of Michigan are studying what makes people overeat in the first place — starting with a small region in your brain that drives you to seek rewards because they feel good.

From an evolution standpoint, this worked great when food was chronically in short supply. Now, when your town has multiple grocery stores and restaurants, all loaded up with the tastiest treats your palate could ever dream up, it’s posing a bit of a problem.

Scientists are taking a look at brain differences to learn why.

Using rat models, researchers looked at the brains of animals that have a tendency to overeat and become obese.

In animals prone to obesity, researchers found glucose took longer to get to the brain’s pleasure area. Instead, they found an excess of an excitatory [icks-site-ah-tory] neurotransmitter.

This means that the balance between how sugar gets broken down in the brain, and the neurotransmitters that are subsequently activated, affect brain activity differently in rats prone to obesity versus rats that are obesity-resistant.

Notably, this means diet is not a factor in whether sugar is processed differently in the rat brains. They either are prone to obesity or they are not.

Future research will delve into the role of inflammation and how it factors into the development of obesity — and how differences in brain function contribute to susceptibility and resistance.