The Neuroscience Of Munchies: Why The Scent Of A Burger Gives Us A High

Enlarge this image toggle caption Todd Plitt/Getty Images Todd Plitt/Getty Images

From cinnamon buns in the morning to a burger after a long run, food never smells as good as when you're superhungry.

Now scientists have uncovered a clue as to why that might be — and it lies in the munchies and marijuana.

Receptors in the brains of mice that light up when the animals are high are also activated when the critters are fasting, French scientists reported Sunday in the journal Nature Neuroscience.

In other words, skipping a meal triggered the same hunger-inducing brain receptors that marijuana does. And it works, at least in mice, by boosting the sense of smell, neuroscientist Giovanni Marsicano and his team at the Universite de Bordeaux report.

That's because the receptors that get activated are located in the smelling center of the brain. And sense of smell is known to be a key factor driving appetite.

In case you're wondering, the mice didn't toke up. The researchers injected the rodents with THC, the active ingredient in marijuana.

Of course, mice aren't men — especially when it comes to smelling. The little rodents spend much more of their lives sniffing out yummy food than we do. And they devote much more of their brain power to the activity.

But there are some hints that a similar mechanism may also be at work in people.

Enlarge this image toggle caption Charlie Padgett/Courtesy of Giovanni Marsicano Charlie Padgett/Courtesy of Giovanni Marsicano

When you skip a meal or fast, your brain creates compounds, called endocannibinoids — appropriate, right? — that look and act similarly to THC. And not surprisingly, these chemicals drive you to eat.

But hunger also makes you more sensitive to food aromas.

Marsicano and his team thought perhaps the two processes — that burning desire to eat (i.e., munchies) and enhanced smelling — were linked. So he and his team went hunting for receptors in mouse brains that controlled both.

They hit the jackpot when they looked in the mice's olfactory bulbs.

That part of the brain was packed with receptors that bind THC and ramp up the rodents' appetite — both when they'd been fasting and when they were high.

These receptors also made the mice more sensitive to odors when their tummies were empty or their brains were stoned.

The data suggest that the major way marijuana triggers the munchies, at least in mice, is through olfaction, Marsicano and his team write in the study.

As for humans? We're a more complicated lot, and there's more than just the sense of smell at play when we get the munchies (from hunger or high). For starters, our "cannabinoid" receptors are located throughout our brains and in other parts of the body.

That said, if the same mechanism does occur in humans, the findings could help scientists develop weight-loss or anti-obesity drugs that target the cannabinoid receptors.

There has already been one such drug, Rimonanbant, approved for use in Europe. But it was withdrawn from the market in 2009 because of serious side effects.