The Holy Grail of addiction science is to fully understand the neurological structures and processes that cause addiction and shape addicts’ behavior. Traditionally, this task was left to psychology, which laid down the core theories based on the symptoms displayed and the behavior exhibited. This is analogous to determining the likely issue with a malfunctioning car based on the sounds emitted from the engine or how it reacts when you push the brakes. Advances in imaging technology—notably through the fMRI (functional magnetic resonance imaging)—have enabled scientists to delve deeper into what’s going on inside the brain and develop a robust understanding of the neurology and biochemistry of addiction. This is like popping open the hood and seeing what’s really going on with the engine.
The Brain – Broken Down
The brain can be split into three sections, based on its evolutionary history. First, you have the brain stem (the reptilian brain), which controls core functions like breathing and the regulation of temperature. This was developed during the earlier stages of human evolution, and is shared with reptiles. Then the limbic system (the mammalian brain) developed along with the first mammals, and controls emotions and the motivation for your behavior.
This makes the limbic system central to the development of addiction, as does its role as the connection between the brain stem and the neocortex, which is the typically “human” part of our brain that is only shared with other higher primates. The fact that ours is much more developed is what separates humans from the other species on the planet in terms of intelligence. The various structures in these three parts of the brain, and the interplay between them, determine who we are.
Addiction And The Reward System
The “reward” system of the brain is the area hijacked by addiction. This is an important region for the brain because rewards are what motivate us to continue to take necessary action. The neocortex may enable us to ask complex questions about the reasons for our behavior, but the lure of the reward system’s neurochemical of choice—dopamine—is enough to ensure we continue to eat food and reproduce. In response to these vital activities, the brain releases dopamine into an area of the limbic system known as the nucleus accumbens, which gives us a feeling of pleasure and thereby establishes some motivation to complete the action again.
Drugs of abuse, and activities such as gambling which are known to be addictive, also stimulate the release of dopamine into this area. This creates a pleasure much more powerful than the natural dopamine surges produced by the brain, and effectively short-circuits the reward system, providing a “shortcut” to the dopamine we’re all motivated by. The reason that only roughly one in10 people is susceptible to addiction is thought to be related to genetic or environmental factors which alter the reaction of the reward system to a behavior or substance that stimulates the release of dopamine.
However, the strong grasp of addiction isn’t explained through this pleasure-seeking mechanism of the limbic system alone. In fact, the interplay between dopamine and another neurochemical, glutamate, is thought to contribute to learning related to seeking a reward. The brain effectively “learns” that the best way to get a hit of dopamine is to take a certain substance or repeat a behavior through these two neurochemicals. The person remembers the positive experiences associated with the drug or activity, and in times of stress this motivates the individual to take the substance or repeat the behavior.
Since the limbic system underpins the motivations and emotions of the entire brain, the higher-level functions of the neocortex can’t easily overcome that desire. The intelligent portion of the brain may be aware of the negative consequences of continued use, but its underlying motivation still comes from the reward system of the limbic region. In other words, behavior is determined by the desire to take the substance when an individual is addicted; always driven by the memory of the pleasure it initially created.
Developing Drug Tolerance
The change that occurs within the brain during addiction causes the development of tolerance. Because the brain is unequipped to deal with such an onslaught of dopamine, it reduces the sensitivity of the reward system. This is described by HelpGuide.org as analogous to turning down the volume on a loudspeaker when the noise becomes unbearable. As a result, the impact of the drug or activity is reduced, because the dopamine it stimulates no longer has as notable an effect. However, the learning process (associating the drug or activity with pleasure) is long established, so the individual still continues with the behavior, often to greater excess in order to achieve the same dopamine hit.
Ultimately, this means the brain is literally dependent on the substance or activity for its feelings of pleasure. The reduced sensitivity to dopamine means that the naturally produced quantities have very little effect, which contributes to a generally negative mood during times of “withdrawal” (when the substance isn’t taken). This is the final piece in the puzzle that makes drug or process addictions such a challenge to break. The brain has to re-adjust the structure and activity of the reward center yet again before some form of normality is re-established.
These factors mean that overcoming addiction is very difficult indeed, and explain why relapses are so common. The brain’s ability to restructure and adapt, however, means that it is wholly possible, and moreover that it gets easier as you go along. The more the brain “unlearns” the association between the drug or activity and pleasure, the more it restructures itself and the more its naturally produced pleasure chemicals have an impact. Deeper understanding of the neurology of addiction may lead to a medical treatment for addiction in the future, but for now, it shows us that overcoming addiction is achievable.