Drug addicts and their nonaddict siblings share the same brain abnormalities linked with poor self-control and drug dependence, a new study suggests.
Researchers looked at pairs of siblings and healthy, unrelated people, and compared their brain structures and their ability to control their impulses — which is known to be compromised among drug abusers.
They found that the addicts and their siblings shared similar abnormalities in the brain, while healthy participants did not have these abnormal traits. They also observed that the siblings performed poorly when it came to tests of their self-control.
Researchers have known that the brains of people addicted to drugs differ from those of others, but it has not been clear whether this is a cause or effect of addiction. The new study, because it shows that siblings who aren't addicted share brain abnormalities with addicts, suggests the brain differences are a cause of addiction, rather than an effect of drug use, the researchers said.
"There is a biological basis why people suffer from addiction," said lead author Karen Ersche, a neuroscientist who researches addictive behavior at the University of Cambridge in England.
"This study suggests that some brains predispose people to become addicted, should they decide to use drugs," Ersche said. "We need to find out how these nonaddicted siblings were able to resist using drugs."
The study was published on Feb. 2 in the journal Science.
Drug addiction, a disease of the brain
Every year, the abuse of illegal drugs and alcohol contributes to the death of more than 100,000 people in the U.S., according to the National Institute on Drug Abuse.
"Drug addiction is the disease of the brain," Ersche said. "It's not a lifestyle choice. It falls in the same category as other psychiatric disorders that are serious and have a basis in the brain."
Previous studies have shown that genes play a role in predisposing people to drug abuse.
"We know through twin studies, if one twin suffers from addiction, the identical twin has a 50:50 chance of also having an addiction," said Dr. Andrew Saxon, an addiction psychiatrist at the University of Washington, who was not involved with the new study.
Why one sibling can become addicted to drugs while the other does not still remains unclear. But Saxon said people's life experiences and environment affect their choices, as well as their brain structures and genes.
"The experiences you have in life could change the structure of the brain, affecting them on a microscopic level," he said.
Same brain abnormalities, different life experiences
Ersche and colleagues studied 50 pairs of siblings — one who had a history of drug addiction, and one who didn't — and compared them with 50 healthy people.
Researchers tested all participants' ability to control their impulses using a "stop-signal reaction time' test, which measures how quickly a person can switch from following one set of instructions to another.
They found that the siblings performed poorly on the test, compared with the other people.
Moreover, brain images revealed abnormalities shared by the siblings that weren’t found in the healthy people. These abnormalities included a decrease in the density of white matter in the front of the brain, which suggests a decrease in self-control, and an increase in gray matter in the middle regions of the brain, which suggests an increased ability to form habits, according to the study.
Saxon said the study provides strong evidence that the brains of drug abusers were different before they started taking drugs. But he also said more research is needed to understand how their siblings were able to resist using drugs.
"People who are addicted to drugs aren't bad people or weak-willed," he said. "They have a disease in their brain that they were either born with or formed during early life that makes them susceptible to using substances in excess."
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