Study of Reward and Addiction

Addiction is a state in which an organism engages in a compulsive behavior which is reinforced or rewarded, even when faced with negative consequences (The Neurobiology of Drug Addiction, NIDA, 2007).

A distinction is generally made between “reward” and “addiction”.

• Reward is defined as a biological mechanism mediating behavior motivated by events commonly associated with pleasure. Reward and motivation can be considered as natural components of normal behavior. Indeed, reward pathways clearly serve to direct behavior towards goals that are beneficial to the organism or species survival, e.g., food and water intake, reproductive activities.
• However, a pleasurable substance can lead to addiction, inducing a compulsive behavior of substance-seeking and intake, a loss of control of limiting intake and the emergence of a negative emotional state when access to the substance is prevented. A variety of substances are susceptible to provoke addiction, such as alcohol, illicit drugs and nicotine among others.

From a mechanistic point of view, drug addiction is a chronic, relapsing disease that is induced by disturbances in the neurobiological mechanisms of brain function. The use of substances for recreational purposes is based on the fact that they cause rewarding effects through the pleasure center in the brain, mainly represented by the mesocorticolimbic dopaminergic pathways.

Chronic drug abuse, however, is associated with a range of adaptive changes in brain physiology. These alterations, which appear to be both intrinsic and extrinsic to the rewarding pathways, gradually lead to the addictive disorder.

Given that drug abuse is a major public health problem calling new therapeutic strategies, animal models have been developed in order to study behavioral and neurobiological basis of addiction. Actual rodent models have predictive validity and are reliable for the study of the addictive potential of substances, the mechanisms underlying the transition from drug use to addiction and the relapse or the individual vulnerability phenomenon.