Neurologic Basis of Addictionby Dr. Heath McAllister
Addiction is one of the realities that human beings have faced for probably tens of thousands of years. Throughout that time, humans have experimented with a whole host of substances found in plants that can lead to a physiologic addiction. Coffee, for example, which was first domesticated in Ethiopia, contains caffeine, which is a highly addictive substance. Green and black teas, which were first cultivated in China, similarly contain this addictive molecule. Caffeine and its related compounds are called methylxanthines and generally function as stimulants in the body. They encompass various other foods and herbs like cocoa and yerba mate.
Similarly humans have used various sedating substances as well that can lead to addiction. A survey of a Neolithic village dating back to 4,000 B.C. provides evidence that humans of that time were using Papaver somniferum, the plant from which we derive all opiate drugs including opium, codeine, vicodin, oxycontin, as well as heroine and morphine. Hydrocodone (Vicodin, Hycodan) is the most commonly prescribed drug in the US and is very effective at blocking the user’s perception of pain. At high doses these medications can cause respiratory failure and cardiac arrest. At sub-lethal doses these are highly addictive drugs that disrupt the lives of over 2 million Americans.
The nature of addiction is complex. There are many psychological factors involved in the development of addiction including a history of abuse, improper role-modeling, insecure attachment to a care-giver as a child. Similarly any history of anxiety or depression can predispose for substance abuse and addiction. These psychological factors cannot be neglected need to be addressed in order to heal addictive tendencies.
From a purely neurological point of view, there are two main players in the genesis and perpetuation of addiction; they are dopamine and serotonin. These are two neurotransmitters that have a broad application in the nervous system, but on a base level we can categorize their actions as such: safety, satiety, and reward. Addictive substances owe their addictive potential to dopamine and serotonin. When a drug is taken, lets say heroin, it triggers a massive surge of dopamine and serotonin to be released. This accounts for the euphoric feelings or ‘high.’ Dopamine is a fascinating substance. When released in appreciable quantities from the nucleus accumbens in the brain, it causes a sense of satiety, satisfaction and comfort. We therefore consider dopamine a reward signal. In human history we would have experienced a dopamine surge when we discovered a source of valuable carbohydrates in the form of vegetables or fruit. In this case humans were experience a sense of reward for contacting something connected to their survival and longevity and therefore it makes sense to reward that behavior. Later humans would experience dopamine release with the ingestion of other calorically rich and addictive substances like sugar and alcohol. This is why when some people experience depressed mood, they will reach for chocolate or ice-cream, to stimulate a burst of dopamine and temporarily relieve their blues.
Serotonin, the other major neurotransmitter that factors into the reward system is similarly released and adds to our feelings of well-being. So from a neurochemical point of view, addictive behavior can be framed as behaviors and activities that induce release of either dopamine, serotonin, or both. Deficiencies of one or both of these neurotransmitters has therefore long been proposed as the neurochemical basis of addiction. Depression has been linked to dopamine and serotonin deficiency. It has also been proposed that people who exhibit risk-taking behavior like compulsive gambling are acting out in order to stimulate dopamine release. Therefore finding healthy ways to normalize and optimize dopamine and serotonin in the brain may be the most effective treatment for addiction.
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