Addiction is a complex disorder that affects the brain in many ways. It is associated with changes in the function of brain circuits involved in pleasure, learning, stress, decision-making, and self-control. Chemical compounds in stimulants, nicotine, opioids, alcohol, and sedatives enter the brain and bloodstream after use. This causes people to lose control of their impulses or want to consume a harmful substance.
Repeated drug use leads to changes in the brain's mesolimbic dopamine pathway, also known as the reward circuit, which begins in the ventral tegmental area (VTA) above the brain stem. Dopamine surges cause neurons to reduce the number of dopamine receptors or produce less dopamine. This results in less dopamine signaling in the brain, such as lowering the volume of the dopamine signal. In some cases, neurons can also die due to toxic drugs.
The brain adapts to these changes by trying to maintain balance. The part of the brain that causes addiction is called the mesolimbic dopamine pathway or reward circuit. Drugs and addictive behaviors are a shortcut, flooding the brain with dopamine and other neurotransmitters. This artificially recreates the effects of dopamine and causes the brain to reduce its production over time.
Images from imaging technology can measure brain and heart function. In drug addiction, the frontal cortex shows less activity than a healthy brain. This is the part of the brain associated with judgment and decision-making. Addiction also causes changes in structure and functioning of the brain.
Scientists have found that brains damaged by addiction have the potential to “unlearn” addictive behaviors. However, due to its delicate structure and chemistry, the brain is also very vulnerable to addiction. People who develop an addiction often find that, over time, the desired substance no longer gives them so much pleasure. Conditioned learning helps explain why people who develop an addiction are at risk of relapse even after years of abstinence. Avoiding people, places, and situations associated with addictive behavior can help reduce the effects of addiction and unhealthy impulses.
Researchers are using technologies such as magnetic resonance imaging (MRI) and positron emission tomography (PET) to understand why some people become addicted to drugs while others don't.An important sign of addiction is that a person continues to use drugs even though this is harming his life. The pleasure associated with a drug or addictive behavior decreases, yet the memory of the desired effect and need to recreate it persists. Addiction reshapes neural circuits to assign supreme value to drugs at the expense of other interests such as health, work, family or life itself.