The Last Word On Nothing

First week of January. Like everybody else in America, I’m on a diet.

I’ve tried lots of diets over the years, and no matter how simple the particular rules — Fat is bad: stick to salads, whole grains and fruit! No no no, fat is good: lay off carbs, and eat lots of meat. Count calories. Count carbs. Are you getting enough fiber? Eat cookies all day! — following them is never easy.

Eating is what neuroscientists call a complex behavior. It’s not reflexive, like a knee jerk or sneeze, but rather depends on lots of brain systems. Real, painful hunger, of course, triggers eating. But so can the smell of bacon, even if you’ve already had breakfast. If you’re starving on a lettuce diet, good old willpower can (I’ve heard) override your urges to eat. And this complexity isn’t just a human thing. For lots of animals, feeding motivations can change with body temperature, sleep cycles and mating opportunities. Dozens of brain regions and hundreds of different kinds of brain cells have been tied to eating.

Which is why this study I’m about to gush about is so (mind the pun) startling. Scott Sternson‘s team from Janelia Farm compelled mice to voraciously eat by switching on just one type of neuron in their brains. Perhaps more provocative, the researchers got mice to completely stop eating by activating a different type of neuron.

Sternson used a fairly new technique called ‘optogenetics’, which is basically mind control (even if most scientists won’t cop to it). They use a virus to insert a light-sensitive protein into particular mouse brain cells. Afterwards, they can use a laser (in the form of a fiberoptic cable running through the skull) to make those cells fire.

Yes, there’s video evidence. In the clip below, you can see the trail of purple-blue light jetting toward the critter’s skull. Its food cup is on the left side. The video has been sped up, and the number at the top indicates how many minutes have passed since the first light pulse. A red box flashes every time the mouse picks up a food pellet.

Crazy, right? The video only shows a few minutes. The experiment actually went on for an hour, and the animals kept on eating and eating and eating.

In contrast, when the researchers activated the second type of neuron, the mice stopped eating. Over a one-day period of stimulation, the animals ate 40 percent less food and lost 7 percent of their body weight, compared with controls.

Sternson is most interested in what these cells do — the chemical messengers they use and how they transmit signals to other cells downstream. (You can read more about this in a piece I wrote for HHMI.) The mechanisms are complex, and the work is far from ready for human applications. Still, you have to wonder: could we somehow turn on these cells in people who eat too much, or too little?

The answer is…probably. Surgeons have implanted metal electrodes into the brains of thousands of people with Parkinson’s disease, severe depression or obsessive-compulsive disorder to directly stimulate specific groups of cells. For some people, this so-called ‘deep brain stimulation’ has saved their lives, relieving tremors, anxiety and dangerous impulses.

It’s invasive and expensive, yes, but the mind control diet would sure be easy to follow.

**

This research appeared yesterday in Nature Neuroscience. The video is courtesy of Scott Sternson.