Drug addiction is a chronic, relapsing brain disorder which is characterised by uncontrollable drug use despite the known harmful consequences. What makes some people more susceptible to developing substance use disorders than others? How do neutral environmental cues become imbued with and maintain the power to produce cravings and promote drug-seeking even after decades of abstinence? I will discuss recent preclinical research which answers these questions by investigating how individual differences in neural activity contribute to addiction-related behaviours.