optogenetics

RECENT POSTS

Sugar On The Brain Circuit: Mice Seeking Sweets May Hold Key To Compulsive Overeating

You know the feeling: you’re tired, cranky, low or just have a serious, relentless desire for something sweet. Part of your brain cries out, “No, don’t do it, this will end badly.” But another (louder) part wants what it wants and won’t let up until that pint of Cherry Garcia, or red velvet cupcake or Caramel Macchiato is in plain sight. It’s an itch that must be scratched.

Now, brain scientists at MIT say they’ve identified a specific neural circuit in mice that can increase that compulsive overeating of sweets, but doesn’t interfere with normal eating patterns necessary for survival. More specifically, turning on this set of neurons drove mice to seek the reward of a sugary drink even in the face of punishment (a shock to the foot); and compelled them to eat voraciously even when full.  When the researchers shut down this pathway, however, the compulsive sucrose-seeking decreased.

Why does this matter? The new research, published in the journal Cell, may ultimately provide a target for the treatment of compulsive overeating and sugar addiction in humans, without undermining the clearly critical drive of eating to live, the scientists say.

“Imagine if I told you that in the future, we could change the way our neural circuits communicate in a way that I did not want to binge on sweets, but still allowed me to eat healthy foods when I’m hungry?” says Kay Tye, the study’s senior author and an assistant professor in the Department of Brain & Cognitive Sciences at MIT. “Obviously there is a ton of work that needs to be done to make this vision a reality, but our study suggests that it is possible.”

A Binge-Free Future?

As obesity rates have spiked in recent decades, experts say that overeating in general and consuming too much sugar in particular are major threats to human health.

But Tye says “the real underlying problems are the cravings that lead to compulsive eating, and the behavior of compulsive overeating itself.”

To tease out what might be driving that compulsion, Tye looked to a particular set of neurons in the mouse brain.

She and her colleagues showed that when mice perform reward-seeking actions enough that they become habits, that activates neurons connecting two key areas: a brain region called the lateral hypothalamus (an area important for hunger, feeding and homeostasis) and the ventral tegmental area (a brain region important for motivation and reward).

“If we want to understand how the brain gives rise to these feelings, thoughts and actions, we need to know more than what they are saying, we need to know who they are talking to,” Tye said. The team used so-called “optogenetic projection-defined phototagging” [essentially using laser light to activate or silence neurons] to see “which neurons…were saying what…and who they were talking to…”

These neural communications are quite distinct, Tye said; for instance, it’s important to distinguish between two types of reward-seeking behavior: binge-eating and drug addiction: “You don’t need cocaine to survive, you need food to survive,” she said.

The “Wanting” Neurons

Tye says that one of the biggest challenges with treating the obesity that comes from compulsive overeating disorders is that “most treatments are just a band-aid — treating the symptoms instead of the core problems.  Gastric bypass for example, is something that just makes it harder to eat, it doesn’t always change a person’s habits and eventually many people relapse and regain the weight.” Again, she theorizes that it’s the craving embedded in the brain that drives the compulsive behavior. She says there may be a distinctive set of  “wanting neurons” as opposed to “liking neurons.” Continue reading