Addiction Becomes a Brain Disease

and subcortical structures that participate both in drug Baltimore, Maryland 21224 reward and in more natural motivational phenomena. For example, Hans Breiter (Massachusetts General Hospital) showed functional magnetic resonance imaging At the end of the decade of the brain, the study of (fMRI) data implicating a generalized limbic and cortical neural mechanisms has come to dominate the study reward circuitry, stressing the nucleus accumbens and of addiction. Whereas attention was once on somatic sublenticular amygdala, in common aspects of drug (co-withdrawal symptoms and liver enzymes, it has turned caine and morphine) reward and monetary rewards and to reward circuitry in the brain and to neuroadaptations in subjective probability assessment. These findings en-in that circuitry that can change sensitivity to addictive courage hypotheses about commonalities between the drugs and that, it is hoped, can explain the compulsive brain mechanisms of addiction and gambling. His data dimension of drug seeking in addicts. The focus on brain implicate this circuitry in drug and nondrug reward ex-mechanisms of reward and addiction began with the pectation as well as in drug and nondrug reward. Nora discoveries of brain reward circuitry in the 1950s and Volkow (Brookhaven National Laboratory) summarized of opioid receptors and endogenous opioid receptors positron emission tomography (PET) studies that show and peptides in the 1970s. Brain mechanisms have now decreased striatal D2 receptors in cocaine abusers, al-become a major focus of addiction research, and addic-coholics, and opiate-dependent human subjects. She tion research has become a major focus of modern neu-also reported decreased levels of monoamine oxidase roscience. The most recent developments in addiction B, an important enzyme in reward circuitry, in smokers. research were highlighted at the December 13–15 Juan The imaging studies suggested multiple cortical and March Foundation workshop on the Neurobiology of subcortical structures participating in drug reward and Addiction; the presented work illustrates how the field more natural motivational phenomena. Such studies fo-has moved—relative to the dominant themes of the cused attention on structures that evolved long before 1970s and 1980s—beyond classical pharmacology, be-the emergence of addiction in human history, structures yond reinforcement, and beyond brain dopamine. implicated in a variety of normal functions and that are the target of recent interest in the field of cognitive neu-Addictive Drugs and Endogenous roscience. Motivational Circuitry The role of one or more of the dopamine systems in Dopamine Reward or Dopamine brain reward mechanisms has been established for over and Reward …