Addiction Is a Complex Brain Disease, Says Volkow
Photo: Leslie Kossoff
Advances in medical imaging have revealed that addiction is a complex disease of the brain, said NIDA director Dr. Nora Volkow.
“By understanding how addiction affects different neuronal processes, we can gather insights that give us a better understanding of why the behaviors of people who are addicted are so disruptive to their lives and frequently that of others,” said Volkow at the Clinical Center’s Contemporary Clinical Medicine: Great Teachers Grand Rounds Lecture held recently in Lipsett Amphitheater.
What nearly every abused drug that results in addiction—whether it be cocaine, alcohol, opioids or nicotine—has in common is not only that they activate the reward circuit of the brain but also that their repeated use modifies the function of the prefrontal cortex. The prefrontal cortex, which is necessary to exert self-regulation and to assign saliency value to stimuli in the environment, doesn’t develop fully until the mid-twenties. The prefrontal cortex, in coordination with the reward circuit, fuels behaviors “that are indispensable for survival.” If a person is hungry, procuring food becomes a salient motivating behavior and eating is experienced as rewarding. Normally, people stop thinking about food once they’ve eaten and food loses its incentive value, which is assigned by the ventral component of the prefrontal cortex (orbitofrontal cortex).
Addiction, however, changes how the prefrontal cortex assigns incentive values to behaviors associated with drug-taking, fixating them. Volkow noted that people who are addicted cannot degrade the intense motivation to take the drug once they have consumed it, which results in compulsive drug-taking behavior. People with addictions often report they can no longer control their behavior, even when taking the drug is no longer pleasurable.
Most drug experimentation occurs before people reach their mid-twenties. Volkow said this reflects the normal development of the human brain. When people are younger, they are learning about the world and experimenting with different things. For many, this might include experimenting with drugs. During this time, adolescents’ brains are rapidly developing and their experiences, including drug-taking, influence some of these developmental changes.
Marijuana, for example, interferes with the endogenous cannabinoid system. Cannabinoids are neurotransmitters that play an important role in nervous system function and in brain development. The consequences of altering a developing brain’s endogenous cannabinoid system during brain development aren’t well-studied but are believed to contribute to future susceptibility to substance use disorders.
In the U.S., the majority of adolescents are exposed to alcohol, about half are exposed to marijuana and another 30 percent are exposed to vaping devices at least once in their lives, she reported.
During childhood and adolescence, the brain is “particularly sensitive to deprivation, social stressors and the effects of drugs,” Volkow said. The environment people grow up in, if adverse, can make them more likely to become addicted to drugs as they transition to adulthood. If the environment is supportive, it can provide them with resilience and protect them against addiction. This explains why adverse environments during childhood and adolescence increase the odds of many diseases and other negative outcomes. Social deprivation, for instance, is one of the worst things that can happen to brain development in children.
“Maximizing that understanding provides us an opportunity to intervene with those children who have been brought up in adverse conditions and to tailor prevention interventions,” Volkow said.
She said researchers are trying to understand why some people exposed to drugs become addicted and others do not.
“There are people [whose genetic susceptibility is] so powerful [that it] can overpower resilient environments, making them liable to addiction,” Volkow said. “There are environments that are so stressful and adverse that [they] can make people vulnerable to become addicted, even though they don’t have the genetic [susceptibility].”
While all drugs activate the dopamine reward neurocircuitry, which in turn modulates the prefrontal cortex, they also have very distinct effects on the brain. Understanding how drugs affect the brain gives researchers the opportunity to develop general as well as drug-specific treatments, Volkow said.
Right now, medications are the most effective treatments for addiction to opioids, nicotine and alcohol. Even though medicine-based treatments work, Volkow said their use is not widespread. The public and medical institutions still see addiction as a choice, rather than a disease.
“If we want to prevent people from taking drugs, we have to ensure that there are social support systems that provide them with opportunities to grow and develop,” Volkow concluded. “If we want to get people to go and stay in treatment and to recover, we need to integrate them into meaningful social environments that respect and accept them. If we don’t, they’ll relapse.”