Researchers at University College London (UCL) have made a surprising discovery about the influence of hunger hormones on decision-making processes in the brain. The study reveals that these hormones directly affect the hippocampus, a key area involved in decision-making and memory.
“We all know our decisions can be deeply influenced by our hunger, as food has a different meaning depending on whether we are hungry or full. Just think of how much you might buy when grocery shopping on an empty stomach.”
“But what may seem like a simple concept is actually very complicated in reality; it requires the ability to use what’s called ‘contextual learning,'” explained study lead author Dr. Andrew MacAskill.
“We found that a part of the brain that is crucial for decision-making is surprisingly sensitive to the levels of hunger hormones produced in our gut, which we believe is helping our brains to contextualize our eating choices.”
In their experiments, the UCL team observed mice in an arena with food and noted the differences in behavior between hungry and full mice.
The researchers discovered that activity in a subset of brain cells in the ventral hippocampus (the underside of the hippocampus) increased as animals approached food, inhibiting them from eating.
However, this inhibitory activity diminished in hungry mice, correlating with higher levels of the hunger hormone ghrelin in their blood. This finding is pivotal as it showcases how ghrelin can cross the blood-brain barrier and influence brain activity to control eating behavior.
The researchers further manipulated this response by experimentally activating ventral hippocampal neurons, making mice behave as though they were full, thus stopping them from eating even when hungry. This was achieved by either activating these neurons or by removing the receptors for ghrelin.
“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,” explained Dr. MacAskill.
The team is now exploring how hunger might affect other aspects of cognition, such as learning and memory, and whether these mechanisms are also involved in responses to stress or thirst.
The researchers hope their findings could contribute to research into the mechanisms of eating disorders, to see if ghrelin receptors in the hippocampus might be implicated, as well as with other links between diet and other health outcomes such as risk of mental illnesses.
“Being able to make decisions based on how hungry we are is very important. If this goes wrong it can lead to serious health problems,” said study first author Dr. Ryan Wee.
“We hope that by improving our understanding of how this works in the brain, we might be able to aid in the prevention and treatment of eating disorders.”
Hunger hormones are crucial in regulating appetite and food intake. The primary hormones involved are:
Often called the “hunger hormone,” it’s produced in the stomach and signals the brain to stimulate appetite. Its levels increase before meals and decrease after eating.
Produced by fat cells, it signals the brain to reduce appetite. Leptin levels rise with increased fat storage, indicating a sufficient energy reserve.
Secreted by the pancreas, it helps regulate blood sugar levels. Insulin also has an effect on body weight and appetite control.
This hormone is released by the intestines in response to eating and promotes a feeling of fullness or satiety.
Produced in the small intestine, CCK is released after eating and helps digest fats and proteins. It also signals the brain to reduce appetite.
These hormones interact in a complex system, balancing hunger, satiety, and energy intake. Understanding their roles can be crucial in managing weight and addressing eating disorders.
The study is published in the journal Neuron.
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