The Neurobiology of Free Will in Addictive Disorders
Nora D. Volkow, M.D.
National Institute on Drug Abuse
Addiction is a disorder that involves complex interactions between a wide array of biological, environmental, and developmental variables. Studies employing neuroimaging technology paired with sophisticated behavioral measurement paradigms have led to extraordinary progress in elucidating many of the neurochemical and functional changes that occur in the brains of people who are addicted to drugs. Although large and rapid increases in dopamine have been linked with the rewarding properties of drugs, the addicted state, in striking contrast, is marked by significant decreases in brain dopamine function. Such decreases are associated with dysfunction of prefrontal regions including the orbitofrontal cortex and cingulate gyrus. In addiction, disturbances in salience attribution result in enhanced value given to drugs and drug-related stimuli at the expense of other reinforcers. Dysfunction in inhibitory control systems, by decreasing the addicted personís ability to refrain from seeking and consuming drugs, ultimately results in the compulsive drug intake that characterizes the disease. Discovery of such disruptions in the fine balance that normally exists between brain circuits underlying reward, motivation, memory, and cognitive control have important implications for designing multi-pronged therapies for treating addictive disorders.