Our brain controls our decisionmaking, letting us know when to go forward with an action and when to stop. Scientists have learned which parts of the brain send these messages. And they know that for addicted people, these "stop" and "go" systems are impaired.
The brain's reward, or "go" system, is basic to all humans. Called the mesolimbic dopamine system, it evolved to help us pursue things necessary for survival such as food or sex. Conversely, the brain's frontal lobes or "stop" system evolved to help us weigh the consequences of our impulses. For example, this system will help keep us from driving through a red light when we're in a hurry, because the brain will tell us that doing so would be both dangerous and illegal. In this case, the "stop" system sends a message that the consequences of doing what the "go" system wants are too negative.
"When things are working right, the 'go' circuitry and the 'stop' circuitry really are interconnected and are really talking to each other to help you weigh the consequences of a decision and decide when to go or not to go," says Dr. Anna Rose Childress, a psychology researcher at the University of Pennsylvania. "It's not that they're separable. They're interactive. They're interlinked at all times." That means that even when you are in a great hurry and risk missing an appointment, you still do not run the red light. "Go" and "stop" have communicated with each other, and "stop" has prevailed.
With Childress's addicted patients, however, "it is as though [the systems] have become functionally disconnected. It is as though the 'go' system is sort of running off on its own, is a rogue system now, and is not interacting in a regular, seamless, integrated way with the 'stop' system."
When an addicted person, even one who is working to recover, gets certain signs, or triggers, such as conflict with a companion, the "go" system overwhelms the part of the brain that's telling them, "Stop! This is a very bad idea!" The trigger can be something essential to the addicted person's life: one recovered writer realized that his addiction was partly triggered by the deadline pressure of his chosen profession as a journalist, and was prompted to start a new career; other recovering people often move from their old neighborhoods to be away from triggers. But a trigger can also be something as subtle as a scent that reminds a person of the place where they used to buy drugs.
When that trigger surfaces, Childress says, "instead of being able to say, 'What? Wait a minute. Think about what happened last week. You lost your job. You almost lost your life,' the 'stop' system doesn't seem to get into the picture at all. It's all about 'go.'"