Neuroscientists May Have Discovered Where in the Brain We Get Hangry

Being hungry can affect everything from our ability to learn and make decisions to our emotions—and that's not just because we're low on energy.

Hunger is the result of a complex interplay of physical and mental processes orchestrated by a hormone called ghrelin. But exactly how ghrelin interacts with the brain has so far remained a mystery. Until now.

"We all know that we make different decisions when we are hungry than when we are not," Andrew MacAskill, a neuroscientist at University College London, told Newsweek. "When I go grocery shopping and am hungry, I will buy all sorts of bad things like chocolate that I wouldn't do if I was full. But how the hormones that signal hunger actually influence the parts of the brain that help us make these decisions isn't really known."

In a study published on November 16 in the journal Neuron, MacAskill and his team put mice in an arena with a serving of food to see how they would behave when they were hungry or full. All the while, the team was imaging the mice's brains in real time to investigate any changes in their neural activity.

"Our study shows that the hippocampus—which is a part of the brain really important for using our memories to make decisions—can actually respond to hunger hormones directly, and this allows the hippocampus to control our decisions based on how hungry we are," MacAskill said.

Specifically, they saw that a subset of brain cells in the hippocampus became more active as the animals approached food. If the mouse was full, this activity was stronger and would stop the animal from eating. However, when the mice were hungry, there was less activity in this brain area so the mice were more likely to eat the food. This reduced activity corresponded with an increase in the hunger hormone ghrelin.

Ghrelin is produced in our gut when our stomach is empty. From here, it enters the bloodstream and travels to our brains, where it stimulates neurons in a region of the brain called the hypothalamus, which is involved in regulating our appetite, heart rate, body temperature and other essential processes.

However, it also appears to suppress activity in other areas of the brain, specifically the hippocampus. So when the researchers removed these ghrelin receptors, activity in the hippocampus increased, causing the mice to act as if they are full and avoid eating the food.

"It appears that the hippocampus puts the brakes on an animal's instinct to eat when it encounters food, to ensure that the animal does not overeat—but if the animal is indeed hungry, hormones will direct the brain to switch off the brakes, so the animal goes ahead and begins eating," MacAskill said.

This hippocampal activity (or lack thereof) may also affect other hunger-related behaviors, like getting hangry.

"The part of the hippocampus we studied is also highly involved in emotion, and so would be an ideal place to combine information about hunger and our emotions," MacAskill said. "This is a really interesting thing to look at in the future!"

These findings may offer insights into the mechanisms of eating disorders and the potential involvement of these hunger hormones and their receptors. The team also hopes to explore more generally how hunger can affect our ability to learn and form memories.

"Our study shows that we can learn to respond differently to cues and events dependent on whether we are hungry or not," MacAskill said. "In other words, hunger can alter how we learn and change how we subsequently interact with the cues and events around us.

"Realizing that hunger can directly influence the way we learn is really important for understanding how our learning and memory can go wrong, for example, in mental illness or in Alzheimer's disease, where previously hunger signaling was not really thought about. Maybe by including hunger in how we think about these problems we can find better ways to treat them."

However, more work is needed to understand how applicable these findings are to humans.

"This work is in mice, and it's not always easy to immediately transfer the findings straight to humans in a simple way," MacAskill said. "But interestingly, it has been known for a long time that diet can influence both our memory and our ability to learn.

"Our research going forward is asking how the workings of the hippocampus we identified in our study might be altered by diet, with the hope that one day we might be able to understand how to better combat these problems."