March 1, 2013
Mental Mechanics Behind Impulsive Eating Present In Both Humans And Flies
redOrbit Staff & Wire Reports - Your Universe Online
The discovery of a neural pathway in the brain of an insect that has been linked to pleasure eating could shed new light on the impulsive consumption of food by men and women, claim researchers from one US university.
As part of their study, University of Georgia (UGA) associate professor of cellular biology Ping Shen and colleagues presented fruit fly larvae that had already been fed with appetizing smells. In turn, those fragrances led to the flies impulsively feeding on sugar-rich foods.
"We know when insects are hungry, they eat more, become aggressive and are willing to do more work to get the food," Shen, who also is a member of the Biomedical and Health Sciences Institute, said in a statement. “Little is known about the other half-the reward-driven feeding behavior-when the animal is not so hungry but they still get excited about food when they smell something great.”
He added that he and his colleagues were “surprised” that a creature like a fly will eat impulsively based upon a reward cue. Their findings, the university explained, suggest that pleasure-based food consumption is a long-ingrained behavior, and that its presence in fly larvae could mean that they could be used to study the neurobiological processes and evolution behind olfactory-driven reward-seeking impulsive behavior.
“To test reward-driven behaviors in flies, Shen introduced appetizing odors to groups of well-fed larvae. In every case, the fed larvae consumed about 30 percent more food when surrounded by the attractive odors,” said April Reese Sorrow, a research writer with the Athens-based university. “But when the insects were offered a substandard meal, they refused to eat it.”
"They have expectations," explained Shen, who along with co-authors Yonghua Wang and Yuhan Pu detailed their findings in Thursday´s edition of the journal Cell Reports. "If we reduce the concentration of sugar below a threshold, they do not respond anymore. Similar to what you see in humans, if you approach a beautiful piece of cake and you taste it and determine it is old and horrible, you are no longer interested."
In order to learn more about the flies´ reaction to the attractive odors, Shen and his team timed how long the insects´ excitement about the potential reward would last. They presented the larvae with a brief smell, and found that the subjects were only willing to wait about 15 minutes to act on their impulses. Beyond that time limit, he explained, their excitement levels would dissipate thanks to a biological mechanism.
Their findings also suggested that the neuropeptides, or the specific brain chemicals responsible for signaling the molecules that trigger impulsive eating, of flies were similar to those found in people. Neurons receive stimuli, convert them into thoughts, and then relay them to other mechanisms which compel creatures to act.
Those molecules are essential for these impulses, the researchers said, demonstrating that the molecular details of such functions are somehow evolutionarily linked between humans and insects.
"There are hyper-rewarding cues that humans and flies have evolved to perceive, and they connect this perception with behavior performance," Shen said. "As long as this is activated, the animal will eat food. In this way, the brain is stupid: It does not know how it gets activated. In this case, the fly says ℠I smell something, I want to do this.'”
“This kind of connection has been established very early on, probably before the divergence of fly and human. That is why we both have it,” he added. "A particular function in the brain of mammals may require a large cluster of neurons. In flies, it may be only one or four. They are simpler in number but not principle."