Drug addiction is a dysregulated motivation illness characterised by severe drug cravings and obsessive drug-seeking. Behavioural neuroscientists have attempted to determine the neurological foundation for several motivational concepts and describe how they are modified by repeated drug use in the hunt for shared neuronal substrates of addiction to different kinds of drugs. The nigrostriatal system, which is engaged in two types of instrumental learning, is one of three major brain systems that play diverse roles in different conceptual aspects of motivation. A frontal cortical area is that which regulates decision-making and motivational processes and a ventral striatal system that is engaged in Pavlovian incentive motivation and negative reinforcement. Drug addiction can cause a shift in striatal circuits from goal-oriented, incentive-based processes to automatic, habit-based responses.
