The Biology Of Addiction

By Dr. Eduardo Pena, MD

EMDR Is Critical In Treating Men's Trauma And Addiction

Some in the addictions field have suggested that addiction is a medical condition like diabetes. Yet, many find the medical view antithetical to a psychological and spiritual view of addiction. Fundamental beliefs about choice and self-determination seem challenged. Although the mind cannot be reduced to neural activity, it is worth taking a look at the biology of addiction and understanding the medical view.

Substance abuse typically begins with experimentation in the early teen years. Experimentation results from the developmental inclination of adolescents to try out adult experiences. Unfortunately, the risk of developing an addiction increases the earlier experimentation begins. With persistent use, there is a change of friends and interests. As abuse progresses into addiction, a fundamental change occurs in the user. What began as a social activity undertaken by choice, becomes a solitary activity undertaken by compulsion. Broken relationships, academic failures, job losses, and arrests fail to deter the addicted user. This end stage of substance abuse is stereotypic. The behavior of a heroin addicted person is similar to the behavior of an alcohol addicted person. The behavioral impairment is milder with tobacco and marijuana, but the overarching pattern is similar – compulsive use. The addicted person no longer feels normal when they are not high. Even the highs have changed. They obtain diminishing pleasure from their substance , increase the doses, combine drugs, and move to more potent delivery methods like intravenous injection. The addicted person begins to hate their drug, yet the addiction becomes increasingly compulsive. Let’s look at what is happening to the brain in this process.

The human brain is comprised of about 100 billion neurons (brain cells), each functioning like a switching station. A spray of neurotransmitter from one neuron reaches across a microscopic gap to bind with the receptors at the receiving branches of the next neuron – the dendrite. This sets off an electro-chemical wave known as an action potential that spreads over the receiving neuron. Depending on the set point of that neuron, that action potential is either stopped in its tracks or propagated down the axons – the firing branches of the neuron. When an action potential does reach the end of an axon, it releases neurotransmitters to other neurons. Neurons arrayed in systems serve specific functions. The limbic system manages memory, mood, and motivation. Within it, the mesolimbic-mesocortical subsystem manages motivation and pleasure. Simplifying, there are three major areas involved in this subsystem when it comes to addiction: the ventral-tegmental area, the nucleus accumbens and the pre- frontal cortex. Imagine you were laboring through your income tax return. After a few hours, fatigue and distress set in. You go to the refrigerator for some refreshments. At first, you only find mundane items: milk, bread, mayonnaise. Then you spy a bakery box! The ventral tegmental area, which responds to stimuli with potentially greater than routine reward, begins delivering dopamine to the nucleus accumbens – the pleasure center. You open the bakery box and find a moist chocolate cake inside. It’s pleasure just looking at it. Dopamine starts to surge in the nucleus accumbens. Now the signal is passed on to the pre-frontal cortex which, as the brain’s executive, has to make some decisions: How many calories can I afford? How much time do I have for this? You judiciously cut out a slice as the pre-frontal cortex closes the loop with feedback to the ventral tegmental area bringing your desire into balance. Your pleasure center (nucleus accumbens) is then stimulated with dopamine with each chocolaty bite. Take note that the circuit was transversed before the first bite. That is because this circuitry is about desire and motivation and not just about pleasure itself.

So what do drugs do to warp this subsystem? Well, imagine that the white powder baked into that moist chocolate cake was cocaine instead of sugar. Cocaine has ten times the potency of sugar in the nucleus accumbens. That pleasure would be hard to resist and with repeated consumption, the nucleus accumbens undergoes a homeostatic down regulation of its dopamine receptors. It reduces the number of dopamine receptors, in an attempt to normalize the dopamine activity. Over time, there is decreasing sensitivity to things that ordinarily would stimulate and motivate. Only drugs of abuse suffice now. The rest of the limbic system adapts through neuroplastic changes to the new priorities. Neuronal connections (via dendrites and axons) instrumental to addiction related behaviors strengthen and those that are irrelevant start to die off. The pre-frontal cortex becomes less active in managing behavior and requires less blood flow and fuel. In distinction to other rewards, like sugar, the attraction to substances does not stabilize in priority but continues to rise in importance. This is why addicts will even risk their safety in pursuit of drugs once their addiction has become severe.

Teens are at greater risk for addiction because their brains are under development. In adolescence, it undergoes a major remodeling wave from the back of the brain to the front. As this wave passes over the limbic system, the nucleus accumbens becomes robust while the pre-frontal cortex is still under construction. The result is an excitable, curious teen without the benefit of a pre-frontal cortex in full control. Mother Nature seems to have created a dicey situation for teens (and their poor parents) but this situation is actually adaptive because adolescence is about independence. Teens would not launch if they did not get excited over their own interests, their own mates, and branch out to create their own lives. The problem is that the developing brain is particularly vulnerable to substances that stimulate the nucleus accumbens.

If substances of abuse affects everyone’s brain in a similar way, why are there such great differences in the propensity to addiction? Well, young people can inherit different risk factors for addiction. Young people who are impulsive, irritable, have trouble with delay gratification, have ADHD or bipolar disorder, are at risk to develop addiction. These conditions reflect an imbalance in the same areas of the brain as is affected in addiction, and make it harder for that person to be satisfied with the ordinary range of stimulation. A child with a predisposition does not inevitably become addicted but under environmental stress like a dysfunctional family or trauma, addiction becomes harder to avoid. We as recovery professionals can only benefit our clients and their families by offering as full an understanding of addiction as possible, including the biological side of the story.

Dr. Eduardo Pena specializes in Addiction Medicine and Addiction Psychiatry and is the medical director at the VA Substance Abuse Department, Recovery Associates and is a Clinical Assistant Professor for NOVA SE University.