Many researchers have noted that hunger and satiety stimulate the brain's reward system. But scientists at Yale University have discovered that the same brain cells behind hunger drive another circuit of reward, the one stimulated by highly addictive drugs like cocaine.
The drive to eat lies in a couple hundred brain cells, called neurons, in the hypothalamus, a tiny structure at the very center of the brain.
"In order for you to feel hungry, these neurons have to be active," said Tamas Horvath, one of the authors of the study published Sunday.
Horvath and his colleagues found that when these brain cells were made to be inactive in the brains of mice, the mice became far less interested in food and became leaner. But at the same time, they became more interested in exploring new environments and they became very interested in cocaine.
The findings, published in the journal Nature Neuroscience, suggest that in mice, and possibly in humans, there is an overlap between addiction and obesity in the brain. But perhaps not in the way many scientists may have thought.
Researchers studying the root of obesity in the brain have suggested that the brain's reward system, which gets jazzed by actions like eating, is less active in animals and people who are obese, meaning they eat more in order to satisfy those brain cells.
But Horvath said his findings suggest the opposite.
"If you make these [brain cells] less active, you're less interested in food, you're leaner, and more interested in novelty and when provided the opportunity for cocaine, you're very interested in cocaine," he said.
So far, the findings apply only to mice, and only more research can show if they apply to humans.
Scott Sternson, who studies the neurological processes behind hunger at Howard Hughes Medical Institute, said the findings are unexpected and mean that scientists need to think more carefully about the wiring of the brain's reward system when it comes to food.
"It will really cause people to look at a new connection between how your body senses your energy levels and how that might affect your response to a drug of abuse like cocaine," he said.
Dr. Deborah Mash, a professor of neurology and pharmacology at the University of Miami School of Medicine, said the findings shake up the current thinking about drug addiction in the brain. Typically, scientists don't consider the bundle of hunger-driving brain cells in the hypothalamus as a part of the system that gets hooked on drugs like cocaine.
"We really don't understand the rules of this system yet," Mash said. "If we could begin to see how the circuitry is disregulated in addiction, we may be able to come up with a druggable target" for treating cocaine addiction.
Mash, who studies the brains of cocaine addicts after their deaths, said the study also highlights some intriguing parallels in human drug addicts.
"Most cocaine-addicted individuals are very thin. When people come off of cocaine, they eat and eat and eat," she said.
Horvath said he will continue to study the overlap between hunger and addiction in the brain, and he hopes that other scientists will consider how even the most fundamental structures of the brain can influence complex behaviors