Mental Health

Eating Even When Feeling Full Happens When Brain's Stop Signal Is Overpowered

Devoured a giant tub of mac and cheese? Finished a tray of cupcakes when you only planned to eat one? Let's face it, we have all had those weak moments where we keep eating despite feeling full.

But why do we do this? Some may wonder if it has to do with the taste or being in an environment that encourages indulgence. But a new study on mice from the University of Michigan (UM) suggests that it all comes down to the brain.

The paper titled "Uneven balance of power between hypothalamic peptidergic neurons in the control of feeding" was published in the Proceedings of the National Academy of Science on Sept. 17.

Feeding behavior has been linked to two clusters of cells known as the POMC neurons and the AgRP neurons, described as next-door neighbors in the brain. If you think of them as being parts of a car, the POMC acts like a brake (letting you know that your hunger has been satisfied) while the AgRP acts like an accelerator pedal (encouraging you to eat more). 

The researchers conducted optogenetic experiments on mice by stimulating the POMC neurons, expecting to see a decrease in appetite. "Instead, we saw a really remarkable effect," said lead researcher Huda Akil, a professor at the UM Department of Psychiatry. "The animals ate like crazy; during the half hour after stimulation, they ate a full day's supply of food."

It appeared that the stimulation had activated both the clusters of cells. This caused a simultaneous release of a "keep eating" signal from AgRP cells and a "stop eating" signal from POMC cells, a bit like using the brake and pressing down on the gas pedal at the same time. 

"When both are stimulated at once, AgRP steals the show," Akil stated, which could likely be the cause of us overeating.

When they tried once again by only stimulating the POMC cells, there was a notable decrease in eating. Furthermore, administrating the drug naloxone blocked the natural opioid system in the brain, resulting in feeding behavior being stopped. 

"This suggests that the brain's own endogenous opioid system may play a role in wanting to eat beyond what is needed," Akil added.

She noted that more research is required to fully understand how perceptual, emotional and social triggers impact our brain and play an important role in overeating. This could potentially help scientists design interventions to tackle obesity, perhaps by activating cells as seen in the new findings, or by other methods relating to the neural system.

"There's a whole industry built on enticing you to eat, whether you need it or not, through visual cues, packaging, smells, emotional associations," Akil explained. "People get hungry just looking at them, and we need to study the neural signals involved in those attentional, perceptional mechanisms that drive us to eat."