Brain research has given us a better understanding of addiction than ever before, and the technology that has developed in the past 50 years has given us an even closer glimpse into the brain structures and functions that contribute to and are impacted by substance use. Although we still have much to learn, we have come to understand some fundamental aspects of addiction that guide modern prevention efforts.
Certain systems in the brain are particularly impacted by substance use.
Although substance use affects all parts of the brain in some way, there are certain parts of the brain that are particularly vulnerable and that become hijacked when a substance use disorder occurs. The first is the limbic system, which is comprised of several structures, such as the basal ganglia and the amygdala. The structure of this system are in charge of our emotional responses, our memory, and our survival instincts. The limbic system is located in the center of our brain, and each time we complete a task that meets our survival needs–such as eating, drinking, having sex, or caring for our young–our brain is flooded with a neurotransmitter known as dopamine, which is a chemical that helps brain cells communicate with each other and reinforces the sensations of reward and pleasure that we experience with an activity. The limbic system then stores that information so that we will remember in the future that we experience pleasurable, rewarding sensations when we perform a certain action. Substance use interferes with the way that neurotransmitters are produced. Some drugs mimic naturally occurring neurotransmitters, confusing the brain and causing it to produce less of a neurotransmitter on its own. Other drugs cause the brain to overproduce natural neurotransmitters, also disrupting the communication between cells.
The second part of the brain that is overridden by addiction is the prefrontal cortex. Located at the very front of the brain, this is the part of the brain that is responsible for higher decision-making, such as weighing the consequences of an action. It is often described as the part of the brain that ‘pumps the brakes’ on the limbic system so that we do not act on instinct alone. It is also the part of the brain that separates us most from other animals.
When substance use starts to become problematic, it is because the limbic system begins to associate the substance use behavior with survival. The brain thinks that it needs the substance in order to survive, and the prefrontal cortex has a difficult time overriding that message in the limbic system. That is why people who experience addiction often do things that negatively impact themselves and others. Although someone who does not have a substance use disorder might question how a person could do things that are destructive and even hurtful, the ability to anticipate the consequences of their actions has been undermined by the substance use.