Striatal ups and downs: Their roles in vulnerability to addictions in humans

► Both increases and decreases in striatal function have been related to susceptibility to addiction. ► We describe a number of factors that could influence whether striatal hyper- or hypo-function is observed in humans. ► A model of addiction is proposed that integrates the influence of these opposite responses. ► Central to this model is the role played by the presence versus absence of addiction related cues.