Addictions, Bad Habits Can 'Highjack' Brain

By the end of January, many New Year's resolutions have been tossed out with leftover holiday cookies and unwanted gifts. It's been nearly impossible to deny that slice of cake after dinner, or to hit the treadmill instead of surfing the Internet.

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Change, especially changing bad habits, is hard -- and rightly so, as any neuroscientist will tell you.

Advances in neuroimaging have enabled researchers to peer inside the brains of addicts and patients with addictive behaviors. They can see, in real-time, what gets patients hooked: how the brain's reward system -- based largely on the neurotransmitter dopamine -- thirsts for more, while inhibitory control centers experience a system failure.

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The pattern is similar across all kinds of behaviors -- from cocaine and tobacco addiction to overeating. That's why changing your mind may be the first step toward breaking a habit, but altering the brain's neural machinery is the real challenge.

Highjacked Pathways

Drugs and addictive behaviors "highjack" the brain's reward system, says Dr. Petros Levounis, director of the Addiction Institute of New York at St. Luke's and Roosevelt Hospitals in Manhattan.

In normal patients, dopamine plays a major role in motivation and reward, surging before and during a pleasurable activity -- say, eating or sex -- to make patients want to repeat a behavior that's crucial to the survival of the species.

Dopaminergic pathways connect the limbic system, which is responsible for emotion, with the hippocampus, which is responsible for memory. This combination etches rewarding behaviors into the brain with strong, even seductive, memories.

The problem arises when the memory and the craving to recapture it take over a person's life.

"Imagine what a stronghold these highjacked pleasure reward pathways take on our brains and our whole existence when they're so closely connected geographically and anatomically speaking with our memories and our emotions," Levounis says.

Then, as the dopamine surge gains speed, the brakes fail. Normal function in the brain's frontal lobes, which are responsible for inhibitory control and executive functioning, or will power, tends to decrease in addicts.

"Ultimately," Levounis says, "the war on drugs is a war between the highjacked pleasure reward pathways that push the person to want to use, and the frontal lobes, which try to keep the beast at bay. That is the essence of addiction."

Similar Patterns

These neural pathways have been well studied in the brains of hardcore addicts. Now, researchers say they see similar pathways involved in other problematic behaviors.

Dr. Gene-Jack Wang, of Brookhaven National Laboratory on Long Island, N.Y., has conducted several brain imaging studies of obese patients using PET scans.

The scans have revealed similarities in brain function -- or a lack thereof -- between patients addicted to cocaine or alcohol, and those "addicted" to eating. When normal patients are injected with a contrast agent designed to be detected by the scanner, it latches onto receptors in the reward center. This causes the PET scan to "light up," revealing an area of red activity in the center of the brain.

But in both drug-addicted and obese patients, the scans show much less red activity because there aren't enough receptors to which the contrast agent can bind. Wang says a decreased availability of dopamine receptors is the brain's way of coping with a constant dopamine overload.

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