Functional MRI (fMRI) is a noninvasive technique that allows us to monitor changes in brain physiology that are based on the increase in arterial blood flow to the local vasculature that accompanies neural activation. Because oxygenated hemoglobin (arterial blood) produces a different magnetic signal than that produced by deoxygenated hemoglobin (venous blood), this is the basis of the BOLD (blood-oxygen-level dependence) contrast used to track changes in regional brain activity at rest or upon stimulation. Imaging studies with fMRI to assess the activation/deactivation responses of the human brain to acute drug administration have reported that in cocaine abusers acute administration of cocaine induced deactivation of the ventral striatum (negative BOLD) that correlated with the high (24). In addition, such studies also reported a negative correlation with BOLD signals in the inferior frontal and orbitofrontal cortex as well as the anterior cingulate cortex (ACC), whereas craving correlated positively with activity in these regions. It is interesting to note that most fMRI studies evaluating the effects of stimulant drugs on reward report a deactivation of BOLD signals in the NAc rather than
