Neurobiology of Addiction

Many psychoactive products can cause addiction. It is curious that despite different pharmacological mechanisms, all these drugs act by releasing dopamine in the nucleus accumbens because of their activity on the brain reward circuit. This stimulation and the resulting positive reinforcement effects are more intense than with more usual rewards. With repetition of their use, drugs cause lasting neurobiological changes within the reward circuit and associated regions. This results in a reprogramming of the neural circuits involved in pleasure and motivation, memory, conditioning, executive functions, judgment, and self-control. These neuroadaptations lead to complex changes in psychological and behavioral functions. Genetic, developmental, and environmental factors influence the course and the severity of the process. To explain this gradual installation of addiction, four major complementary mechanisms, which unfold and reinforce each other, are necessary: motivational awareness, learning habits, hedonic allostasis, and inhibitory control deficit (impairment of executive functions). Tolerance to the reinforcing effects of natural rewards is observed alongside awareness of the motivational effects of drugs and the stimuli associated with their use. Behavior is increasingly oriented exclusively toward seeking and consuming drugs. The absence of drugs is accompanied by negative emotional behaviors, signs of withdrawal, “craving” (intense desire to use), which are key elements of a relapse.