The next time you find yourself eyeing up the snack cupboard 10 minutes after finishing dinner, it might help to know that a simple overactive appetite may not be the culprit. A new study in mice has found a brain circuit driven by cells dedicated to seeking out tasty food, and scientists suggest it could exist in humans too.

The neural circuitry in question was found in a region of the brainstem called the periaqueductal gray (PAG), an evolutionarily ancient part of the brain that has retained similar functions in mice and humans.

“Although our findings were a surprise, it makes sense that food-seeking would be rooted in such an ancient part of the brain, since foraging is something all animals need to do,” said corresponding author Avishek Adhikari, associate professor of psychology at UCLA, in a statement. 

The PAG is usually more associated with panic and fear responses – in both humans and mice, when the entire region is activated, it can cause a “dramatic panic response” according to Adhikari. However, during their investigation, the team found that stimulating just a specific cluster of cells in the PAG induced foraging and feeding behavior in the mice.

They achieved this by injecting mice with a genetically modified virus that caused their brain cells to produce a light-sensitive protein. A fiber-optic implant then allowed the scientists to selectively activate the modified cells using light, a technique called optogenetics. A miniature microscope developed at UCLA could then be fixed to the mouse’s head to record the neural activity.

When the cell cluster within the PAG was stimulated, the mice went into food-seeking overdrive. They chased live crickets, which are a prey species for them, and were just as interested in non-prey foods and in investigating non-food items within their enclosures.

They also showed a preference for fatty, high-calorie foods – so much so that they were willing to endure a mild electric shock to get at a tasty walnut, something that’s not normal mouse behavior. 

“The results suggest the following behavior is related more to wanting than to hunger,” said Adhikari. 

“Hunger is aversive, meaning that mice usually avoid feeling hungry if they can. But they seek out activation of these cells, suggesting that the circuit is not causing hunger. Instead, we think this circuit causes the craving of highly rewarding, high-caloric food. These cells can cause the mouse to eat more high-calorie foods even in the absence of hunger.”

The scientists also tested the opposite scenario, genetically engineering the food-seeking cells to have reduced activity under exposure to light. These mice didn’t show interest in foraging, even when they were actually hungry.

“This circuit can circumvent the normal hunger pressures of how, what and when to eat,” summarized Fernando Reis, the postdoctoral researcher who designed the study and performed the bulk of the experiments.

While these results are limited to mice for now, we know that similar cells exist in the PAG of the human brain. The team suggests that if activation of the circuit has the same effect on us as on our rodent friends, it could play a role in understanding eating disorders.

A lot more work is needed to iron out how much of this applies to humans – but it’s curious to think that when you find yourself looking for something sweet after a big meal, it might just be your brain, rather than your belly, that’s the source of the craving. 

The study is published in the journal Nature Communications.