Decision-making has also been studied in cocaine-dependent subjects using fMRI. Bjork and colleagues (2008) compared neural signals in a heterogenous group of drug-dependent individuals and controls while performing a risk-taking task. Guaranteed reward activated the head of the caudate in drug-dependent participants but not in the controls. The predecision signal in the posterior mesofrontal cortex was also blunted in drug-dependent participants compared to controls, suggesting that substance dependence is characterized by a combination of striatal hypersensitivity to reward and reduced recruitment of conflict monitoring circuitry when reward is associated with potential penalties (Bjork et al., 2008). Another study (Goldstein et al., 2007a) used fMRI to compare cocaine-abusing individuals and controls in response to gradients of monetary rewards. Cocaine abusers showed reduced regional signal to differences between across the reward gradient, and that prefrontal cortex sensitivity to money was associated with motivation and self-control within cocaine abusers but not controls. A second study by the same group showed that lower subjective sensitivity to reward gradients significantly correlated with enhanced signals to monetary reward in the lateral orbitofrontal cortex, inferior frontal gyrus,
