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Addicted to Novelty
B.J. Casey, director of the Sackler Institute for Developmental Psychobiology at the Weill Medical College of Cornell University, has been exploring the way people of different ages respond to rewards and risks by scanning them as they play games. In a recent study, Ms. Casey and Adriana Galvan, a former doctoral student, had subjects perform a task on a computer in which they could win $25. If subjects answered a question correctly, either a single coin or a big pile would appear on the screen.
In scans of all ages, the coins set off a deeply buried area of the brain called the nucleus accumbens, a region that responds to various types of rewards. The adolescent accumbens seemed particularly primed for big payoffs. The region lit up especially brightly when teenagers saw the pile of money, and it showed an anemic response to the single coin, when compared with adults, the Cornell group reported in the Journal of Neuroscience last summer.
Other researchers have found similar activity in this particular brain region. A team at the National Institutes of Mental Health in 2005 saw that the accumbens responded more in adolescents than in adults when they received a reward.
Ms. Casey says it makes sense that the adolescent brain is primed to seek rewards and take risks. "From an evolutionary perspective," she says, "the only way you're going to leave your comfortable village and go out and mate somewhere else that isn't going to be as safe as to be a risk taker."
To understand why the accumbens might be acting up more in adolescence, researchers are looking into how younger brains deal with dopamine, a key neurotransmitter molecule produced by some neurons to send signals to other nerve cells. From studies on animals, researchers know that the dopamine system is intimately connected with the way mammals respond to rewards.
"A lot of things we do naturally, like sex and food, will cause dopamine to squirt into the nucleus accumbens," says R. Andrew Chambers, an assistant professor of psychiatry at the Indiana University School of Medicine, who uses rats as a model to study substance abuse in human adolescents.
Pleasure is not the only sensation that gets the dopamine system going. In rats, novelty has a powerful effect on the adolescent brain. "When an animal is put in a place where it's never been, the dopamine system operates about as robustly as when it gets a hit of cocaine," says Dr. Chambers.
Evolution may have tuned the mammalian reward system to seek out new experiences, whether it be trying an unknown food or exploring a foreign region, he says. "It is so powerful for mammals because it's so critical for survival," he says. "This is what's going to tell you what the resources and dangers are around you."
Dr. Chambers suggests that the dopamine system of adolescents might react so strongly because the prefrontal cortex is still developing. Neuroscientists call this trait plasticity, and it confers benefits as well as risks. It helps explain the creativity of adolescence and early adulthood, before the brain becomes set in its ways. But it also makes adolescents more prone to addiction, says Dr. Chambers.
"The conditions in the brain, the circuits that mediate motivation and addiction, are so plastic and so influenced by addictive drugs that the motivational disorder can take hold more aggressively during that period," he says.
At least that's the story for rodents. At present, researchers have gained most of their knowledge about the dopamine system from work on animals, because they need to use invasive techniques to monitor this molecule. But some investigators are starting to study the genetics underlying dopamine activity in humans.
That is why when Erika first arrives at the Pittsburgh lab, an assistant scrapes the inside of the girl's cheek to collect some cells. By analyzing Erika's DNA, the research team will check what variations of genes she carries for regulating the strength of the dopamine signal. Ahmad R. Hariri, an assistant professor of psychiatry and director of the developmental-imaging genetics program at Pitt, has yet to examine the data his group is collecting for adolescents, but he has started to find some intriguing links in adults. "We have some exciting preliminary findings showing that the genetic variations in dopamine-related genes do in fact predict the variability in the reward circuitry," he says.
As they gather more data, Mr. Hariri will try to extend the research to adolescents to see if the pattern persists between particular genetic variations and an exaggerated reward system. In the long run, such findings could suggest ways to better prevent or treat problems such as addiction, he says.
Internet Addiction and Psychopatology
- Mustafa KOC. Internet Addiction and Psychopatology. The Turkish Online Journal of Educational Technology, Jan2011, 10(1), p 143-148.
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