Monday, December 2, 2013

Addiction in the Spotlight at Neuroscience 2013

Testing treatments for nicotine, heroin, and gambling addiction.

Several addiction studies were among the highlights at last month’s annual meeting of the Society for Neuroscience (SfN) in San Diego. Studies released at the gathering including therapies for nicotine and heroin addiction, as well as some notions about the nature of gambling addiction.

And now, as they say, for the news:

Transcranial Magnetic Stimulation (rTMS), the controversial technique being tested for everything from depression to dementia, may help some smokers quit or cut down, according to research coming in from Ben Gurion University in Israel. Abraham Zangen and colleagues used repeated high frequency rTMS over the lateral prefrontal cortex and the insula of volunteers. Participants who got the magnetic stimulation quit smoking at six times the rate of the placebo group over a six-month period. Work in this area is limited, but there is some preliminary evidence that some addictions may respond to this form of treatment.

Speaking of the insula—a site deep in the frontal lobes where neuroscientists believe that self-awareness, cognition, and other acts of consciousness are partially mediated—research now suggests that out-of-control gamblers may be suffering, in part, from an overactive insula. People with damage to the insular region are less prone to both the “near-miss fallacy (where a loss is perceived as “almost” a win) and the “gambler’s fallacy (where a run of luck is “due” to a gambler after a string of losses). The volunteer gamblers played digital gambling games while undergoing functional MRIs. Luke Clark of the University of Cambridge, along with researchers from the University of Iowa and the University of Southern California, uncovered a “specific disruption of both effects” in a study group with insula damage. This ties in with earlier research demonstrating that smokers with insula damage lost interest in their habit. This one remains a puzzler, and further research, that brave cliché’, is needed, especially since disordered, or “pathological” gambling is now classified in the DSM5 as an addiction, not an impulse control disorder.

And speaking of stimulation, if you go deep with rat brains, you can stimulate a drug reward area and reduce the motivation for heroin in addicted rats. Deep brain stimulation (DBS), an equally controversial treatment approach, now in use as a treatment for Parkinson’s and other conditions, is a surgical procedure involving the implantation of electrodes in the brain. When Carrie Wade and others at the Scripps Research Institute and Aix-Marseille University in France electrically stimulated the subthalamic nucleus and got addicted rats to take less heroin and become less motivated for the task of bar pressing to receive the drug. Earlier work had demonstrated a similar effect in rats’ motivation for cocaine use. “This research takes a non-drug therapy that is already approved for human use and demonstrates that it may be an option for treating heroin abuse,” Wade said in a prepared statement.

Too much stimulation leads to stress, as we know. And George Koob, recently named the director of the National Institute on Alcohol Abuse and Alcoholism, discussed his work on the ways in which dysregulated stress responses might act as triggers for increased drug use and addiction. Koob focused on the negative reinforcement of stressful emotional states: “The argument here is that excessive use of drugs leads to negative emotional states that drive such drug seeking by activating the brain stress systems with areas of the brain historically known to mediate emotions and includes the stress/fear-mediating amygdala and reward-mediating basal ganglia.” For Koob, “stress can cause addiction and addiction can cause stress.”

Finally, hardcore gamblers show a boost in reward-sensitive brain areas when they win a cash payout, but less activation when presented with rewards involving food or sex. The study features more volunteers playing games inside fMRI machines, and purports to demonstrated that problem gamblers are less motivated by erotic pictures than by monetary gains, “whereas healthy participants were equally fast for both rewards.” This “blunted sensitivity” in heavy gamblers suggests the possibility of a marker for problem gambling, in the form of a distorted sensitivity to reward, said Guillaume Sescousse of Radboud University in The Netherlands, during a mini-symposium at the conference. “It is as if the brain of gamblers interpreted money as a primary reward…. for its own sake, as if it were intrinsically reinforcing.”

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