2023-11-17 08:13:05
What if hunger was driving our decisions? A team of scientists explains what happens in our brain and why this ‘reaction-action’ mechanism is possible and important, underlining how we risk serious health problems when something goes wrong. What experts have observed is that a hunger hormone produced in the gut can have a direct impact on the area of the brain where decisions are made, so as to guide behavior. Scientists at University College London (UCL) verified this in mice. And their study, published in ‘Neuron’, is “the first to demonstrate how hunger hormones can directly impact the activity of the brain’s hippocampus when an animal is considering food.”
“We all know that our decisions can be profoundly influenced by hunger, as food has a different meaning depending on whether we are hungry or full – observes the study’s lead author, Andrew MacAskill -. Just think about how much you could buy while shopping on an empty stomach. But what may seem like a simple concept is actually very complicated and requires the ability to use a process called ‘contextual learning’. We discovered that a part of the brain crucial for decision making is surprisingly sensitive to hormone levels hunger, produced in our gut, which we believe helps our brain contextualize our food choices.”
So is there a control room assistant in the intestine? For the study, researchers placed mice in an arena with food and observed how they behaved when hungry or full, all while investigating their neural activity with real-time imaging. All the mice spent time examining the food, but only the hungry animals would start eating. The researchers focused on brain activity in the ventral hippocampus, a part of the brain that makes decisions and is believed to help us form and use memories to guide our behavior. The scientists found that activity in a subset of brain cells in the ventral hippocampus increased when the animals approached food, and this activity inhibited the animal from eating. But if the mouse was hungry, the neural activity in this area was less, therefore, the hippocampus no longer prevented the animal from feeding. The researchers found that this corresponded to high levels of ghrelin, the hunger hormone, circulating in the blood. (continued)
To shed further light, the UCL researchers activated ventral neurons in the hippocampus and were able to make the mice behave as if they were full, leading them to stop eating even if they were hungry. The scientists achieved this again by removing the receptors for ghrelin, the hunger hormone, from these neurons.
Previous studies have shown that the hippocampus of animals, including non-human primates, has ghrelin receptors, but there was little evidence about how these receptors work. This discovery shows how ghrelin receptors are used in the brain, noting that the hunger hormone can cross the blood-brain barrier (which strictly prevents many substances in the blood from reaching the brain) and directly impact the brain to drive activity, controlling a circuit in the brain that is likely the same or similar in humans. “It appears that the hippocampus puts the brakes on an animal’s eating instinct when it encounters food, to ensure that the animal does not overeat. But if the animal is really hungry – the researchers explain – the hormones will direct the brain to turn off the brake, and then the animal goes forward and begins to eat.”
Scientists are now investigating another aspect: whether hunger can impact learning or memory. Further research, they say, could also shed light on whether there are similar mechanisms at play for stress or thirst. “Being able to make decisions based on how hungry we are is very important. We hope that by improving our understanding of how it works in the brain, we might be able to help in the prevention and treatment of eating disorders,” concludes the first study author, Ryan Wee.
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