Craving for alcohol and drugs in animals and humans: biology and behavior.

Research studies indicate that sites and pathways for appetitive drive states, that are located in the limbic system, appear to be responsible for normal and pathological craving for alcohol and other addicting drugs. Pathological craving for alcohol and drugs in humans has been substantiated by animal studies, which have identified neurosubstrates and neurotransmitters associated with behavioral models of addiction. Repetitive administration of alcohol and drugs appears to affect hedonic homeostasis of the appetitive drives leading to the hedonic alleostasis where negative reinforcement exceeds positive returns despite continued drug use. Neuroimaging studies have concentrated on areas in the brain related to reward or reinforcement of alcohol/drug use, but the technique can be employed to find support for a neurosubstrate to distinguish normal craving or "liking" from pathological craving or "wanting" a drug. Identifying the neurobasis of "wanting" a drug long after not "liking it" is central to understanding pathological craving and loss of control over drug use in addiction in humans. Neuroimaging is currently the only method to directly visualize sites for craving in the brain in humans. Neuroimaging techniques will provide methods, which are not possible in animals, for studying addictive disease in humans.