Addiction and the Brain
The human brain is a marvelous mechanism. It is responsible for the vast majority of all the behaviors we produce; only specific types of reflex actions are not under the direct control of the brain. Numerous research studies and books have been devoted to brain behavior relationships. The study of addictive behaviors and how they affect the brain has become one of the most researched topics in neuroscience, biological psychology, and psychiatry. The findings from many of these studies have been compiled under headlines or titles such as “The Addicted Brain.” It is important to remember that brains do not become addicted, but instead people become addicted.
While the understanding of brain behavior relationships is certainly an important aspect of understanding addictive behaviors, it is also a mistake to reduce complex behaviors like addiction to mere biological processes. Nonetheless, in order to understand addictive behaviors, one needs to have a basic understanding of how addictive behaviors and drugs affect the brain.
Understanding the Reward System
One of the seminal studies leading to the understanding of the neurobiology of addiction occurred in 1954 by James Olds and Pete Milner. These researchers discovered that rodents would learn to repeatedly press a lever when a particular area of the brain was electrically stimulated (the septal area, an area deep in the brain that is involved in numerous functions, including the experience of reinforcement). When other areas of the brain were stimulated, the rodents would not repeat this behavior at all or would not repeat it as vigorously as they would when the septal area was stimulated. The septal area became known as the pleasure center of the brain.
Later research identified what has been often referred to as the reward system in the human brain. The two major neurobiological pathways in the reward system are the mesolimbic pathway and the mesocortical pathway. Both pathways utilize the neurotransmitter dopamine as their primary neurotransmitter (a chemical substance that allows the nerves of the brain, the neurons, to communicate with one another) and are two of the four major dopaminergic (dopamine-utilizing) brain pathways in the human brain.
The mesocortical brain pathway is believed to be involved in certain aspects of thinking (particularly in directing intended behaviors), emotional behaviors, and motivation. The mesolimbic pathway is involved in motivation (particularly directed at getting reinforcement [rewards]). Both of these pathways have extensive connections throughout the brain but have numerous connections to the frontal areas of the brain. The frontal lobes of the brain are responsible for numerous complex behaviors, including movement, abstract thinking, problem-solving, and directing attention. Much of the current theory regarding how addictive behavior recruits areas of the brain to produce compulsive behaviors focuses on aspects of these dopaminergic pathways.
Drugs of abuse activate these pathways, and the activation of dopamine in the brain pathways results in many individuals wanting to repeat these behaviors as a result of the types of euphoric effects that dopamine activation produces. Repeated activation of the neurons in these brain pathways results in structural changes in the brain. This leads to the activation associated with drug use generalizing over a number of different situations. The connections become stronger, the anticipation of reward becomes more salient, and individuals become increasingly motivated to repeat behaviors that they are reinforced for performing, such as drug use. Over time, the brain becomes more efficient at tasks that are repeated, and the activation of dopamine in these brain pathways can occur when the individual thinks about using their drug of choice, is in an environment that reminds them of using their drug of choice, becomes stressed and anxious and looks to relieve that tension, etc. Eventually, some individuals begin to experience severe issues with judgment and impulse control as the altered connections in these brain pathways may become so strong that they override many of the person’s rational capabilities.
Some drugs, like stimulant drugs (e.g., cocaine, methamphetamine, Ritalin, etc.), directly result in massive increases of dopamine in an individual’s brain due to their mechanism of action. Individuals who develop substance use disorders to these types of drugs are experiencing a sort of double whammy: They experience the changes in the dopaminergic pathways in the brain that occur with any type of addictive behavior and the changes that occur as a result of the direct activation of dopamine by these particular drugs. Once these changes in the brain have occurred at a specific level (as a result of chronic abuse of drugs), they may never fully resolve. Structural changes in the brain as a result of experience will remain to some extent even if the individual ceases to use drugs. Thus, chronic drug abusers are always at an increased risk to relapse if they begin using drugs again because their brains have become “hardwired” to the effects of drugs. As a result of these alterations in the brain, many biological-based researchers like psychiatrists and addiction medicine physicians, and even individuals without a strong biological background who deal with people who have suffered from severe substance use disorders, have accepted the notion that addiction is a brain disease. Certain researchers and addiction treatment providers maintain that in severe cases of addictive behaviors, individuals lose their decision-making capabilities and are unable to choose not to be addicts.
The mechanism by which the brain changes as a result of experience is not unique to the use of drugs. Neuroplasticity, the phenomenon that occurs when the brain changes as a result of experience, occurs over numerous different types of cognitive and learning experiences, physical activities, and even detrimental experiences, such as repeated severe emotional stress. For instance, individuals who have spent years mastering some type of athletic skill, such as hitting a baseball, will retain many of the alterations in their brains that have occurred as a result of repetitive practice and reinforcement over the years. Even if the individual stops playing baseball for several years, their skills will return to them much more quickly if they decide to resume playing compared to an individual who has never played the game before.
This tendency to relearn once-mastered tasks at a significantly increased pace or level is actually functional. Neuroplasticity helps individuals benefit from previous experiences even if they occurred long ago, as demonstrated in the classic memory experiments by Hermann Ebbinghaus who was able to determine that he could relearn long forgotten material that he once had mastered at a far quicker pace than he could learn new material.
Not Only Dopamine
Numerous research studies have indicated that dopamine is a major neurotransmitter that is involved in nearly all forms of addictive behaviors. Nonetheless, dopamine is not the only neurotransmitter that is affected by addictive behaviors. Some substances have their primary effects on other neurotransmitters in the brain. In addition to the activation of the dopaminergic pathways mentioned above, these brain pathways also become repetitively activated and may become permanently altered. For example:
- Alcohol is known to activate the inhibitory neurotransmitter gamma-aminobutyric acid (GABA), and it blocks the action of the excitatory neurotransmitter N-methyl-D-asparate and serotonin.
- Benzodiazepines like Xanax and Valium work primarily on activating GABA.
- Opiate drugs like heroin and morphine activate enkephalins and endorphins, which are neurotransmitters associated with reducing the subjective experience of pain and stress.
- Tobacco products activate the nicotinic cholinergic brain receptors in the brain.
The brain pathways associated with these neurotransmitters also undergo significant structural changes in addition to changes associated with the activation of dopamine as a result of any reinforcing effects that occur with chronic drug use. Structural changes that occur as a result of substance use/abuse may also present as structural damage to areas of the brain.
Massive releases of neurotransmitters are often followed by massive depletions of these neurotransmitters in the brain. The cycle of massive neurotransmitter release and depletion can induce significant wear and tear on many of the neurons in the brain, resulting in significant damage. In addition, substances like alcohol and cocaine are severely toxic and can produce damage to tissues that are exposed to them. When brain tissue is exposed to these substances repeatedly, significant damage can occur. The brain does have some ability to repair itself, but even mild to moderate levels of neuronal damage cannot be fully repaired, and when neurons die in this manner, they are most often not replaced.
Why Is It So Difficult to Quit?
Individuals who have been diagnosed with a substance use disorder, professional clinicians who have treated someone for a substance use disorder, or friends and family members of an individual with a substance use disorder understand the difficulty that occurs when someone tries to quit using their substance of choice. One of the main issues in treatment and recovery is preventing relapse. Several theories explain why individuals give into cravings and cues.
- The notion of priming in addiction refers to how the brain becomes activated by small reminders or clues to past addictive behaviors. These small reminders, such as environmental cues, emotional states, and even the experience of stress, can help to re-trigger the emotional and perceptual experiences that one had while one was using drugs. These events actually occur in the brain and result in the activation of the specific neural pathways that were involved in the individual’s drug abuse, making the experience of cravings extremely hard for many individuals to ignore.
- Positive incentive theories refer to the anticipated pleasure that relieving cravings will induce once a person uses their drug of choice. Interestingly, the actual level of pleasure individuals receive from drug use often diminishes over time, and it is the anticipated pleasure of using drugs that drives individuals to reuse the drug. Individuals often continue to habitually abuse drugs or alcohol to capture the memory of the initial experiences they had when they first used these drugs as opposed to the actual experiences they get from subsequent use.
- Incentive sensitization theory capitalizes on the above finding that as an individual develops tolerance to a drug, the actual pleasure they receive from using the drug decreases. Individuals with substance use disorders often continue to crave the drug for the anticipated relief/pleasure/euphoria that they expect to get from the drug as opposed to the actual effects they receive from using it. It is not the act of using itself that drives relapses but the desire to use again.
- The development of physical dependence that occurs with chronic use of some drugs also represents a significant motivating factor for individuals to continue using drugs. Physical dependence consists of both the syndromes of tolerance and withdrawal. Withdrawal symptoms can be extremely unpleasant for individuals who use specific types of drugs, such as alcohol, opiates, benzodiazepines, and stimulant drugs. Individuals may continue to use drugs to avoid withdrawal symptoms, and the continual use of drugs develops increased tolerance, which results in a strengthening of the withdrawal syndrome itself. Thus, individuals become caught in a vicious cycle of drug use to avoid negative withdrawal symptoms (negative reinforcement). As a result of their continued drug use, they strengthen their potential to develop even more severe withdrawal symptoms by developing increasing levels of tolerance (which results in them continuing to use more and more of the drug in an attempt to get the effects they once got at much lower doses).
Is Addiction a Brain Disease?
The notion that addiction is a brain disease, most often supported heavily by medical doctors, addiction treatment professionals with biologically based backgrounds, and even 12-Step groups like Alcoholics Anonymous, is not as universally accepted as many people are led to believe. However, numerous research studies continue to identify biological associations with addictive behaviors and to further specify specific biological issues associated with the abuse of specific classes of drugs. These findings continue to fuel the brain disease model of addiction, and many non-biologically-based mental health workers who treat addiction primarily with psychotherapy techniques have been won over to the notion that addiction represents a chronic brain disease.
Briefly, the major tenets of the disease model of addiction include:
- The identifiable alterations that occur in the brains of individuals with substance use disorders as revealed by neuroimaging studies
- The obvious self-destructive behaviors that individuals with substance use disorders engage in
- The notion that individuals with substance use disorders often have cognitive issues with judgment and decision-making that are believed to have occurred as a result of significant alterations in the brain pathways associated with these cognitive tasks
- Alterations in the brain that are believed to rob the individual of their ability to choose whether or not to use their drug of choice
There are numerous objections to the disease model of addiction from healthcare professionals at all levels. Part of the controversy regarding this issue is the use of the medical definition of the term disease. If the term were used in a metaphorical matter, these critics would not object.
According to critics, addictive behaviors as diagnosed by the criteria developed by the American Psychiatric Association (APA), do not meet the medical definition of a disease as they do not have a primary measurable deviation from a physiological anatomical norm. No one can be diagnosed with any type of addiction through any form of medical testing in the same way that cancer, diabetes, communicable diseases, etc., can be diagnosed. In addition, addictive behaviors are self-acquired; they cannot be transmitted, are not contagious, and have no identifiable heritable component that can be used to aid in their diagnosis or recognition or to reliably predict who will develop an addiction. Finally, current treatments for addiction may involve the use of some medically assisted treatments, but the primary treatment is simply to help individuals stop their behavior.
Interestingly, a recent article in the New England Journal of Medicine by two of the major disease model proponents Dr. Nora Vokow and Dr. George Koob attempted to reclassify the disease model to apply primarily to individuals with a diagnosis of a severe substance use disorder as specified by the APA diagnostic criteria for substance use disorders. This article almost appears to represent an attempt by these esteemed researchers to compromise their original position that “addiction is a brain disease” to “addiction is a brain disease in certain individuals.” This muddies the whole picture. Moreover, this article also seems to rule out individuals who are diagnosed with behavioral addictions, such as compulsive gambling disorders, as having brain diseases because the specifications in the article of what types of addicts have actual brain diseases would not apply to behavioral addictions.
The bottom line is that addictive behaviors are very complex behaviors that develop as a result of the interplay between biological, psychological, and social factors. While it is clear that addictive behaviors are associated with significant changes in the neurobiology of an individual, it is also clear that an element of choice plays an integral part in developing an addiction and in one’s recovery from an addiction. Despite significant research evidence that indicates that addictive behaviors are associated with numerous changes in an individual’s brain, it may very well be that simply labeling addiction as a brain disease results in an oversimplification of the issue.