Study finds clue about brain's binge and addiction triggers

A relatively unstudied region of the brain may play a key role in binges and addictions, according to new research.

A group of scientists found that suppressing activity in key areas of the brain appeared to lessen addictive and reward-seeking behavior in rats, and that the results may one day help show how to control addiction in humans.

A view of a rat's brain; the ventral pallidum, where researchers showed that binge behavior can be suppressed, is in the red-stained roughly triangular areas toward the bottom.
Source: Jocelyn Richard | JHU
A view of a rat's brain; the ventral pallidum, where researchers showed that binge behavior can be suppressed, is in the red-stained roughly triangular areas toward the bottom.

The ventral pallidum is a region of the brain that has been thought to play a role in addiction and reward-seeking behavior, but it has not garnered the same attention as other brain regions in addiction research.

However, a team of researchers from universities in the United States and France found that the region appears to drive the reward-seeking behavior associated with addiction, and that suppressing the region helps suppress learned addictive behaviors.

The team published its results in the June 15 edition of the peer-reviewed journal Neuron.

In the experiment, the researchers played various sounds — sirens and beeps — for different rats, and trained the rats to press a lever whenever they heard a specific sound. When a rat pressed a lever after hearing the right sound, the lever dispensed a small serving of sugar water.

"External cues — anything from a glimpse of powder that looks like cocaine or the jingle of an ice cream truck — can trigger a relapse or binge eating." -Jocelyn Richard, lead author of study

The team fitted the rats with sensors that measured their brain activity. In most of the brain regions they studied, such as the nucleus accumbens, about 20 percent of the brain cells increased their activity when the rat heard the sound prompting it to press the lever for the sugary reward. But in the ventral pallidum, a full 70 percent of the region's brain cells increased their activity.

"That really surprised us," said Jocelyn Richard, the lead author on the study and a post-doctoral fellow at Johns Hopkins University. "We weren't expecting to see such a large percentage" of cells in that region make a jump in activity when rats were prompted by sounds, Richard told CNBC in an interview.

That may say a lot about the way stimuli in an environment drive addictive behavior.

"External cues — anything from a glimpse of powder that looks like cocaine or the jingle of an ice cream truck — can trigger a relapse or binge eating," Richard noted in a release accompanying the study. "Our findings show where in the brain this connection between environmental stimuli and the seeking of food or drugs is occurring."

They then used a process called optogenetics, whereby they shined beams of light into the brains of the rats to suppress activity in the ventral pallidum.

Sure enough, when they "switched off" that region of the brain, the rats were far less likely to go after the sugar water when the sound played. And when they did, they did so more slowly. The rats were not as interested in the things that had appeared rewarding before.

Richard pointed out the ventral pallidum activity was not just registering the sounds the rats were hearing. It was actually driving their reward-seeking behavior.

Richard's team carried out a laboratory study with rats — not humans living their everyday lives — so important limitations come to bear: There are, for example, huge biological and behavioral differences between the two species. In addition, Richard said, the rats were not "especially unhappy." They weren't starved for food, and there was no reason to think they were emotionally distressed or depressed. So a human addict out in the world may experience psychological or outside factors that bear different results.

But there are important similarities between the two species that suggest the study's results are promising. First, Richard noted that the brain circuitry in the studied region is similar in rats and humans.

In addition, "rats also like a lot of the same things humans like," Richard said. They like sugar, for example, and they can become addicted to some of the same drugs, such as cocaine and heroin.

And, she added, the results of research studying addictive behavior in rats has often been supported later in human studies.