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Neuroscience of overeating: Animal study provides insight

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Scientists identify a part of the brain that is important for the initial stages of learning to seek food. David Sacks/Getty Images
  • Overweight and obesity increase the risk of a wide range of illnesses, including type 2 diabetes, cardiovascular disease, and some types of cancer.
  • Research in rats has identified a part of the brain involved in the early stages of learning to seek out and eat food when presented with specific cues.
  • Insights into how the brain develops unhealthy eating habits could inspire new ways to reduce overeating.

The prevalence of obesity has almost tripled globally since 1975, according to the World Health Organization (WHO).

By 2016, 39% of adults around the world had overweight, and 13% had obesity.

The problem is particularly acute in the United States, where the Centers for Disease Control and Prevention (CDC) report that the prevalence of obesity among adults was 42% in 2017–2018.

Overweight and obesity are associated with cardiovascular disease, metabolic syndrome, type 2 diabetes, and severe COVID-19. They also increase the risk of certain types of cancer.

The WHO blame what they call the global obesity epidemic on declines in physical activity, and rising consumption of energy-dense food.

Healthcare professionals recommend a range of simple behavioral strategies to reduce overeating, such as smaller portion sizes, eating more slowly, and keeping calorific snacks out of sight in the kitchen.

However, as in many other animals, our brains have evolved to maximize energy intake.

An international team of scientists led by the University of Florida in Gainesville has discovered that a region of the brain called the infralimbic cortex (IL) plays a role in the initial learning of food-seeking and food self-administration behaviors.

People tend to overeat when they are exposed to environmental cues that remind them of treats, said Dr. Sergio Iñiguez, one of the researchers who directs the Iñiguez Behavioral Neuroscience Lab at the University of Texas at El Paso.

He claims that this is one reason people opt for dessert even after a filling meal. So, a glimpse of the sweet treats on a dessert trolley might tempt people even if they are full.

The researchers discovered that they could reduce overeating in rats that had just learned to associate edible treats with a particular cue. The scientists did this by switching off activity in the animals’ IL, which is part of the medial prefrontal cortex near the front of the brain.

“This is a big discovery because we now have experimental tools that allow us to turn off neurons while the subjects engage in a specific behavior,” said Dr. Iñiguez.

“This research shows that a specific part of the prefrontal cortex of the brain is important for the initial stages of learning to seek food.”

In the long term, the discovery could lead to the development of new ways to prevent overeating in humans.

The findings appear in the journal eNeuro.

The scientists first trained rats to press a lever to receive a food pellet. When the rats pressed the lever, the food was delivered and, at a same time, a light switched on, which was the cue.

In order to identify the earliest stages of food-related learning in the brain, the scientists compared activity in the brains of animals that learned quickly with those that took longer.

They discovered that mini-circuits, or “ensembles,” of neurons in the IL were much more active in the fast learners than in the slow ones.

When the researchers blocked the activity of these neuron ensembles in the fast learners, the animals became less likely to press the lever to receive food when the light came on.

The authors conclude:

“Considered together, these data suggest that IL neuronal ensembles are formed during the acquisition of food self-administration behavior and that these ensembles are necessary for the expression of food-seeking behavior. These experiments may shed light on the neurobiological underpinnings of food memories and motivation to acquire food.”

It is worth noting that the main objective of this research was to test theories about what happens in the brain during food-related learning rather than to develop clinical applications to reduce overeating.

In addition, what happens in the brains of lab rats as they learn how to acquire food may not accurately reflect what happens in human brains in real-world situations.

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