The Neurobiology of Free Will and Drug Addiction SAN DIEGO —Advances in brain-imaging technology have shown what many researchers have long suspected—that drug addiction is a disease of the brain, and not simply a failure of free will. One of the most instrumental leaders in that effort has been Nora Volkow, MD. The sometimes controversial work of Dr. Volkow and others during the past 15 years has provided a better understanding of how neurobiological changes in the brain can lead a person to lose control over his or her behavior and become addicted to drugs. That research and understanding may soon yield more effective medications and better overall treatment for patients with addiction, said Dr. Volkow at the 2007 Annual Meeting of the American Psychiatric Association.
A primary focus of addiction research has been the dopaminergic system, as drugs of abuse increase dopamine in limbic areas of the brain, which can then trigger a sensation of pleasure. “But what has become clear is that dopamine is not just about pleasure,” said Dr. Volkow, Director of the National Institute on Drug Abuse in Rockville, Maryland. Imaging studies have shown that multiple systems in the brain are affected by long-term substance abuse, including those relating to motivation, drive, memory, inhibitory control, and what we perceive as salient. Drug use can lead to plastic changes in the brain that “ultimately underlie the compulsive drug intake and loss of control that causes drug addiction,” said Dr. Volkow.
In an early study that challenged the reward theory of drug addiction, Dr. Volkow used positron emission tomography to observe the effects of IV methylphenidate in persons addicted to cocaine and in healthy controls. She found that the subjects addicted to cocaine had a reduced amount of dopamine released in the striatum when given IV methylphenidate and a reduced “high” relative to that of controls. Persons addicted to cocaine also had an increased thalamic response associated with craving—a finding not observed in controls. “What we documented was that the controls and the cocaine addicts differed not just in terms of the qualitative response to the drug, but they actually had a quantitatively different response,” said Dr. Volkow. “So contrary to what we hypothesized—that cocaine abusers would report a more intense high than controls—we saw exactly the opposite.”
In a recently completed, but as yet unpublished, study comparing 20 alcoholics and 20 healthy controls, Dr. Volkow found that the amount of dopamine released in alcoholics was 70% lower than in controls, “indicating, indeed, that decreases in reward circuitry are not just specific for cocaine,” she noted.
. . . . . .
_________________________________________________________________
