Have you ever had “one of those days,” when you succumbed to the temptations of the seventh of the Seven Deadly Sins and indulged in a little chocolate gluttony? A day when you managed to eat an entire chocolate cake, or an entire family-size bag of M&Ms? Be honest now…we’ve probably all been there and done that at some point in our lives.
On the other hand, even during these occasional moments of gluttony, few of us have ever managed to eat 5% of our total body weight in chocolate at one time. But in a fascinating experiment conducted at the University of Michigan and reported in the journal Current Biology, laboratory rats were enticed into doing exactly that. Given the rats’ tiny size and weight, this is equivalent to a 150-pound human eating 7.5 pounds of chocolate in one sitting. That’s a hunk of the sweet, brown stuff about the size of an American football.
There is an area of the brain that seems to control gluttony
The U.M. biopsychologists who managed this weren’t mad scientists trying to create The Rat Who Ate Ann Arbor. They started by studying a region of the brain called the neostriatum, located in humans below the cortex and behind the eyes. The neostriatum is known to control motor behaviors and movement, but it is also located in the same neighborhood of the brain as the areas that control our reward mechanism, the impulses that urge us to continue behaviors that the brain considers pleasurable or rewarding.
Suspecting a link between the neostriatum and these “reward centers” with regard to appetite, the researchers sampled fluids from this area of the brain while the rats were at rest, hungry, being presented with food, eating it, and after eating it. The food in question was one of the rats’ favorites – M&Ms. For some reason they like the little nuggets of sweetness as much as we do.
They noticed surges of a neurotransmitter called enkephalin – an opioid that produces sensations of pleasure – when the rats began feeding. The stronger the levels of enkephalin rose, the more the rats were tempted to eat the M&Ms. However, the rats soon became sated and stopped eating after a maximum of 10 M&Ms. The researchers then painlessly injected an artificial opioid into the neostriatum, to see what that would do. The rats essentially began a feeding frenzy, wolfing down as many M&Ms as they could, often twice as many as usual.
What does all this mean?
Well, for the scientists conducting the study, it meant that they had definitively demonstrated that one particular region of the brain was in control of mammals’ occasional tendencies to indulge in gluttonous behavior. When the neostriatum becomes flooded with opioid substances – either artificial as in this experiment or natural as a result of our own brain chemistry – the neostriatum puts our appetites into overdrive and we react by eating until we physically can’t any more. Neuroscientists have theorized that this might be a trait left over from our past as foragers or hunter-gatherers. If we stumbled upon a source of food, it made sense from an evolutionary point of view to eat as much of it as possible at one time, so that other animals wouldn’t find it and eat it before we could. According to this theory, the brain pumps natural opioids into the neostriatum and essentially stimulates a kind of survival-inspired heightened appetite, during which we can eat more than usual.
What this means for us, and the occasional desires we experience to devour a football-sized bowl of M&Ms ourselves, is not as clear. Hopefully in the future researchers can take this new information about how the brain influences gluttony, and find ways to help us not fall prey to it.