Jan. 31, 2010 -- 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.

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.

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.

"If a person constantly has an excess of dopamine, the brain will down-regulate," Wang says, explaining the principle commonly referred to as "tolerance." "Once the system is down-regulated, we have to do more in order to get the same amount of feeling in our normal state."

Thus, obese patients "will want to eat more in order to compensate for their down-regulated system."

In other experiments, Wang and his colleagues have also found that a higher body mass index (BMI) correlated with lower prefrontal cortex function -- the area associated with inhibitory control.

Those studies also revealed that a higher BMI was liked to a decrease in memory and executive functioning.

"If they're obese," Wang said, "they have a problem controlling their eating behaviors."

Out of Control

Ed Susman was 293 pounds when he became a patient in a clinical trial of an investigational weight loss drug. He chronicled his year-long experience in a series of articles for MedPage Today.

Eating, to him, was a "compulsion" -- as was biting his nails, a habit he picked up at age four.

Over the course of the trial, not only did Susman lose 52 pounds. He also stopped chewing on his fingertips.

Medications Help Treat Some Behaviors

He doesn't yet know if he was on the drug or on a placebo. But he strongly suspects he wasn't feeling a placebo effect.

"I believe I was on the drug because it controlled a compulsion that I had for 50 years," Susman says of nail-biting. "This stopped it cold."

Unfortunately, he says, the same didn't happen for his eating habits, but he's only gained back 10 of those 52 pounds in the year he's been off the trial.

The drug was Lorcaserin -- a combination of benzazepine and hydrochloride, two neurological agents. Susman says the drug is "supposed to improve your willpower, your ability to overcome compulsions."

Lorcaserin works through the serotonin system, which regulates appetite, mood and motor behavior.

But two other investigational obesity drugs target the dopamine reward system -- Contrave, which is a combination of bupropion and naltrexone, and Qnexa, which combines phentermine and topiramate.

"Some medications that have used similar dopamine modulation, until now, have failed," Wang said. "These two companies are using the command of the modulation of the dopamine system with other neurological systems, such as the opiate or norepinephrine system. According to the trials, they've been very effective."

Wang called the new medications "a bright light for the treatment of obesity."

Kicking the Habit

Basically, the idea of medications that act on the dopamine system is "to cool down those reward pathways," Levounis says. There are two strategies for doing so: an agonist strategy, or an antagonist strategy.

The agonist strategy is "feeding the beast, providing activity in the cell so that the cravings go down," Levounis said. Classic examples are nicotine patches, or methodone for opioid dependence.

On the other hand, the antagonist strategy is to block the receptors. Naltrexone, for example, will block opioid receptors so that the drug addict won't feel anything if he or she attempts to get high.

"After a while, you say, 'This is not worth my time, my money, my trouble,' so you stop using," Levounis explains.

While these have been the two main strategies in addiction pharmacotherapy, there's now a "third avenue" -- the partial agonist approach.

The parital agonist is one molecule that blocks most receptors while still providing just a little bit of an "oomph" to calm cravings. That's how varenicline (Chantix) helps smokers quit, and how buprenorphine gets junkies off heroin or other opioids.

Therapy Key to Overcoming Addictions, Compulsive Behavior

But what about inhibitory control? Susman believes he was given the active drug -- Locaserin, which is designed to dial down the "high" he receives from food -- during his 12 months in the study. But, it should be understood that there are no medications that are capable of ramping up will power.

"It's an area of active research," Levounis says. "There are some medications proposed, but nothing to write home about."

He said treatment is typically two-fold. For addicts, psychiatrists will cool down the reward pathways, often with medication. Then, they target the diminished frontal lobes.

"We try to beef up the frontal lobes as much as we can, and we do that with psychotherapy," Levounis said.

Researchers agree that psychotherapy is key to regaining self-control, and it's the predominant treatment used in patients with addictive behaviors.

Mark Smaller, a psychoanalyst in private practice in Chicago, said psychotherapy often reveals an underlying cause for an addiction or compulsive behavior. Usually, it's anxiety or depression.

Acknowledging those problems may help change behaviors. Once they're realized, a patient can start working against them, with the help of the brain's own neuroplasticity. Essentially, neurons can disconnect and re-connect, or loosen their connections and tighten them, which often manifests in noticeable change.

"[Psychological] insights can actually begin to change brain chemistry and diffuse compulsions," he said. "If you address those issues, you can have a positive impact on your life that can change the chemistry of your brain."

Smaller said it "creates a new psychological -- if not neurological -- structure that can help regulate behavior."

Though research on neuroplasticity is relatively young, the idea of "rewiring" the brain is not new. Too often, it's been an excuse for indulging, an explanation for a New Year's resolution deferred: "I can't stop eating chocolate, I'm just not wired that way."