What Part of the Brain is Altered By Addiction?

Addiction and brain change go together. Pathological changes in brain function that result from substance abuse cause the skewed decision making common to addicts.

The primary system in addicts’ brains that’s physically different than those of non-addicts is the brain’s “Reward System.” (Scientists refer to it as the “Limbic System.”) This network is responsible for the feeling of pleasure. It’s also responsible for both positive and negative emotions, which is why drugs have the ability to alter one’s moods.

Brain cells, known as neurons, communicate through the exchange of neurotransmitters. The primary neurotransmitter that stimulates the Reward System is called dopamine. If enough dopamine is released into the brain’s reward circuits, euphoria results.

Dopamine-based exhilaration is a common experience, at least partially responsible just about anytime one experiences pleasure. “A hug, a kiss, a word of praise or a winning poker hand”1 can trigger a dopamine spike. When your team pulls out an improbable victory at the last second — think Joe Montana, Dwight Clark and “The Catch” — the delirium you feel if you’re a 49er fan is the rush of dopamine stimulating the brain’s Limbic system. By contrast, the crushing disappointment felt by Cowboy fans was, at least in part, the result of dopamine depletion.

Drugs over-stimulate the Reward System by increasing dopamine many more times than natural rewards. In turn, the brain reacts defensively to the overstimulation by developing tolerance, which results in physical changes to brain cells in the Reward System. These changes alter not only the structure of those neurons, but also their function, changing the way the brain operates and how addicts think.

The Reward System isn’t only about feeling pleasure. It’s also centrally involved in learning from rewarding experiences by remembering them in order to repeat them. That is, dopamine is also crucial to motivation. The brain changes in dopamine function associated with addiction thus skew motivation, explaining addicts’ over-sized drive to continue drug use despite negative consequences.

The Reward System is an ancient part of the brain, pre-dating the evolution of rational brain networks. Thus, though the altered addict brain often acts irrationally, it may be more accurate to describe those behaviors as pre-rational.

For a more detail on how drug abuse alters the Reward System, click on Drugs, Dopamine and the Reward System.

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