Understanding the Disease Model of Addiction

It is hard for some to accept that addiction may be a disease. After all, there is no virus that will give you insatiable cravings for alcohol, and no bacteria will force you to snort heroine. Why is it, then, that most medical associations recognize addiction as a disease of the brain?

Some clarity may be gained by defining what is meant by “disease.” According to Mariam-Webster’s Dictionary, a disease is “a condition of the living animal or plant body or of one of its parts that impairs normal functioning and is typically manifested by distinguishing signs and symptoms.”

Going on this definition, we can say that addiction can be classified as a brain disease if (1) it has a definable set of symptoms, and (2) it causes the brain to function abnormally. The first criteria is easy: the symptoms of addiction involve a loss of control over the taking of a particular substance or the engagement in a particular behavior. That leaves us with one last question: does addiction change the brain in such a way that impairs normal functioning?

To answer this question, we first have to understand what a healthy brain looks like.

Homo Sapiens Sapiens – The Ape with Two Brains

The actual scientific name our species is “Homo Sapiens Sapiens.” One way to translate this might be “Smart, Smart Man.” Admittingly, it is a bit hubristic. But it is also fitting, since we essentially have two brains.

The oldest part of our brain is the limbic system. This is the part of the brain that we share in common we all higher order animals. It is the job of the limbic system to keep us alive by motivating us to seek out the things that aid in our survival (pleasure) and to avoid the things that threaten it (pain). When we experience a source of a pleasure, such as food or sex, the limbic system creates a powerful memory that links that feeling to the behavior that lead to it, motivating us to repeat the behavior. The same can be said of the avoidance of behaviors that lead to pain.

The newest part of our brain is the neocortex, which literally means “new brain.” When the neocortex evolved, it didn’t replace the limbic system, it grew on top of it, so that the two coexist inside our skull. Part of the neocortex is the prefrontal cortex, located behind the forehead, which gives us our ability to reason, to make judgements, to plan ahead, and, most importantly, to squash the impulses emanating from the limbic system.

Limbic Hijackings – When the Primitive Brain Takes Over

The prefrontal cortex wins this battle much of the time. But since it is the limbic system’s job to keep us alive, and since that is more important, from an evolutionary standpoint, than either our goals or society’s expectations, the limbic system has veto power over the prefrontal cortex in situations in which it believes our survival is in jeopardy. And, because the limbic system is the more primitive brain, it can be fooled; the threats that it perceives aren’t always real.

In the book “Emotional Intelligence,” psychologist Daniel Goleman describes a particular subset of such an event, which he calls an “amygdala hijacking.” The amygdala is part of the limbic system, and it is that part of the brain responsible for our experience of emotions. Goleman describes how extreme emotions such as anger or fear can cause the amygdala to temporarily overpower the prefrontal cortex and take control. These emotions are a response to some perceived threat, and they drive us to act on base instinct to either neutralize or escape that threat (fight or flight response). When the threat is over, and the prefrontal cortex reasserts dominance, we can often be shocked at our own actions.

Another type of limbic hijacking can be experienced if you try to hold your breath until you pass out. You will find that it is impossible; at some point, the limbic system will panic, take over, and literally force you to breath.

The limbic system and the prefrontal cortex are constantly vying for control in something of a neurobiological counterpart to what Freud described as the tension between the id and the ego; the limbic system fights to have our primal urges satisfied while the prefrontal cortex fights off these limbic hijackings in order to have us behave according to social convention and our own long-term goals.  If the limbic system had complete control, we would be little more than animals. Yet, without it, we wouldn’t be motivated to do anything, including working, socializing, or even eating. In a state in which the brain is functioning normally, this leads to an uneasy partnership between the two brains, in which we learn to satisfy our urges in socially acceptable ways (i.e. sex in the context of marriage, sweets in moderation, non-violent expressions of anger, etc.).

Addiction and the Neurological Balance of Power

When someone develops an addiction, certain physical changes occur in the both parts of the brain which tip the balance in the limbic system’s favor. For information on how specific drugs effect the brain, click here.

The Disease of Addiction and the Limbic System

When the limbic system creates a link between a certain action and a sensation of pleasure, it does so by releasing a chemical called dopamine. The more intense the pleasure¸ the larger the release of dopamine. The larger the release of dopamine, the stronger the motivation to repeat the behavior that caused that pleasure will be.

The things that we humans are susceptible to becoming addicted to are classified as “super stimuli.” This means that the level of dopamine that they cause to be released is beyond that which we would experience in a natural environment.

Our brains are not evolutionarily designed to handle this. The addictive substance or behavior quickly becomes the largest source of pleasure that the limbic system knows and, because it associates pleasure with keeping us alive, it is effectively tricked into believing that we will die if we go too long without the drug or behavior that we are addicted to. Once this happens, going too long without that taking that drug or engaging in that behavior becomes solid ground for a limbic hijacking, by which we are forced do so. Moreover, because neurons that fire together wire together, as this happens again and again, the neural wiring which the limbic system uses to veto the prefrontal cortex is strengthened to an unnatural level as well.

The Disease of Addiction and the Prefrontal Cortex

Dopamine also plays a role in the functioning of the prefrontal cortex. In a sense, the prefrontal cortex “runs” on dopamine, as it causes the neurons that make it up to become activated. In fact, a genetic predisposition towards low dopamine production is believed to be behind ADD and ADHD, which are both conditions that involve a chronically underactive prefrontal cortex. In the brain of an addict, there is plenty of dopamine, but the repeated release of massive amounts of it causes the brain’s dopamine receptors to become fatigued, impairing their ability to respond to the chemical. That’s why, over time, the addict needs more of their drug of choice to feel the same level of pleasure, the same “high.” For the prefrontal cortex, this means an impaired ability to use dopamine to activate itself.

If this goes on long enough, the neurons in the prefrontal cortex start to atrophy. This leads to a condition that scientists call “hypofrontality;” if you were to compare the brain scan of a long-term addict to that of an average person, you would see that their prefrontal cortex is physically smaller, as well as less active. This means that, not only does the addict experience a loss of the ability to say “no” to addiction cravings and to fight off the ensuing limbic hijacking, but he also experiences a more general loss of impulse control. This is why addicts behave so recklessly.

Conclusion: Addiction is a Progressive Disease

Thus, we see that addiction causes the brain to be physically altered in such a way as to prevent it from functioning naturally, satisfying the second criteria for being called a disease. While it can be argued that the first time that addict participates in his addiction is a choice, the more he does so, the more these brain changes set in, increasing the limbic system’s ability to take control while decreasing the prefrontal cortex’s ability to fight back.

Thus, addiction is not only a disease, it is a progressive disease, which means that, left untreated, it always gets worse. Every time the addict gives in, it lowers his ability to resist the temptation the next time around by that much more, while increasing his tolerance and making him crave even more of his drug of choice. When powerfully addictive substances or behaviors meet with the right genetic predisposition and psychological makeup, it can only take one “hit” to get that person started on the downward spiral that is addiction.