Neurobiology of Addiction 

Addiction is a debilitating disorder affecting how the brain perceives pleasure and reward. As the National Institute on Drug Abuse notes, “addiction is defined as a chronic, relapsing brain disease that is characterized by compulsive drug seeking and use, despite harmful consequences.” The neurobiology of addiction is of increasing interest to researchers and clinicians alike, as understanding the mechanisms of addiction continues to play a crucial role in effective drug addiction treatment. 

The purpose of this article is to provide an overview of the neurobiology of addiction and the brain’s reward system, through discussing the alterations that occur in the brain’s reward system in the progression of addiction.

The Brain’s Reward System 

At its core, the reward system is comprised of multiple neural pathways involving a number of brain structures and neurotransmitters. The primary reward system of the brain is the mesolimbic dopamine (DA) system, which is often referred to as the brain’s “reward system.” This pathway is a regulator of behavior and motivation, as it helps us to understand where and how to obtain rewards. This reward system encodes behaviors and memories related to rewards, and, in turn, bring about connecting memories and behavioral memories. Examples of reward activities include food and water for gaining sustenance, sex for mating, and money for achieving financial stability. The overall reward system can be engaged by primary, natural rewards, and secondarily, by the abused drugs which activate the reward system directly.

Pathways of Drug Action 

The most commonly abused drugs, such as cocaine and opioids, act on two pathways of the mesolimbic DA reward system: the ventral tegmental area (VTA) and the nucleus accumbens (NA). In the VTA, DA neurons link the prefrontal cortex, amygdala and hippocampus brain regions to the NA, one of the principal brain regions associated with reward processing. The NA is critical for reward-seeking behavior and powerfully mediates the rewarding effects of drugs of abuse like opioids. Moreover, this connection indirectly affects the hippocampus, which is strongly associated with memory formation.

Neurotransmitters Involved in the Reward and Arousal Pathways 

The primary neurotransmitters involved in reward and arousal pathways are dopamine and opioids. Dopamine and opioids are neurotransmitters that are released by the brain, either naturally to produce a pleasurable response to a reward, or from the ingestion of drugs, to produce a powerful and euphoric reward. Specifically, dopamine is a neurotransmitter involved in producing pleasurable sensations and reactions to rewards, while opioids help to reduce stress and produce a calming effect.

Alterations in the Brain’s Reward System as a Result of Addiction 

Addiction is a powerful and complex disease that take root in the brain’s reward circuitry. It is the body’s inability to receive enough pleasure without taking drugs, due to changes in the reward pathways of the brain. With repeated drug use, the brain adapts to the overwhelming surges in dopamine by producing less dopamine or fewer dopamine receptors. As a result, someone who has been abusing drugs will feel less pleasure, and will be unable to enjoy the same activities that once gave pleasure prior to Addiction, leading to feelings of guilt, sadness or loneliness.

Neuroadaptations Due to Prolonged Substance Abuse 

In addition to decreased receptor sensitivity to dopamine, chronic drug use produces multiple other neuroadaptations in the brain’s reward system. Chronic drug abuse disrupts the brain’s internal reward system, leading to altered pathways and brain chemistry. Over time, neurons may become desensitized to dopamine, reducing their response to pleasure, and leading to a constant sense of dissatisfaction as the addict is unable to receive the same pleasure as before. As a result, someone with an addiction will depend more and more on drug-induced pleasure, leading to addiction. This can also cause a compulsion to seek out drugs, as the brain seeks out a higher dopamine level to make up for the lost dopamine sensitivity.

Impacts of Neurobiological Changes on Decision Making

The neurobiological changes that occur in the dormant reward system of an addict significantly interfere with decision making and other aspects of behavior. Addicts may become fixated on obtaining and consuming drugs, endorsing risky behaviors in their attempts to achieve it. This may include sacrificing friends, family or job stability to acquire drugs. As most of the changes to the brain would already be taking place before addiction sets in, it is difficult to prevent these alterations from happening.

Consequences of Addiction 

The consequences of addiction manifests in a myriad of ways. Addicts can suffer from serious physical harm, mental health conditions, such as depression and anxiety, as well as financial and social problems. These physical and mental health deficits can be further compounded by other conditions that arise as a result of heavy drug use, such as infectious diseases like HIV and Hepatitis B and C.

Treatment for Addiction 

Addiction is not a lost cause, however. Treatment for addiction ranges from behavioral therapies such as cognitive behavioral therapy, to approaches such as contingency management and twelve step facilitation. Medications such as methadone and buprenorphine are also used to manage the withdrawal symptoms of addiction. Further, alternative ways of dealing with addiction such as exercise, yoga, and mindfulness meditation may also play a potential role in treating addiction.

The understanding of the underlying neurobiology of addiction continues to expand, with advances in understanding the reward pathways, the hormones and neurotransmitters involved, and the way in which neural changes in the brains of addicts alter their decision making and inclination towards craving drugs. Addiction is a chronic, relapsing brain disease that is characterized by compulsive drug seeking and use; however, with a comprehensive treatment plan, recovery is possible. The more we understand the neurobiology of addiction, the more we can develop effective and sustainable treatments for this complex disorder.