How addictions change the brain
Addictive substances release dopamine into the nucleus accumbens, a part of the brain associated with motivation and pleasure. In the past, researchers thought dopamine simply registered pleasure in the brain, prompting a person to want more and more of the substance. But more recent research suggests that dopamine interacts with another brain chemical called glutamate. After exposure to a habit-forming drug, these chemicals work in the brain not only to signal pleasure, but to prompt the person to seek out more of the substance as well.
According to one theory, repeated exposure to an addictive substance causes nerve cells in the nucleus accumbens and the prefrontal cortex — the area of the brain involved in planning and executing tasks — to communicate. This communication links pleasure with action, so the person not only wants the drug, but he or she has the motivation to go and seek it out.
Two other parts of the brain—the hippocampus and the amygdala—store information about environmental cues associated with the desired substance. This way, the person can use those cues to find the substance again. For example, if a person usually drinks alcohol at a bar, his brain will link the pleasure of drinking with the sights, smells, and sounds of a bar. These memories help to create a conditioned response—or craving—whenever he sees, hears, or smells those environmental cues again. It’s the brain’s way of “remembering” that the cue might mean that the addictive substance is nearby.
