The activation patterns noted between the groups during this masked affective task underscore the likelihood that individuals who have smoked marijuana process emotional information in a different way from those who do not smoke, which may result in negative consequences. These data suggest differences in affective processing in chronic smokers even when the stimuli are presented below the level of conscious awareness. The cingulate has been hypothesized to play a critical role in the evaluation of the motivational significance of emotional stimuli (Devinsky et al., 1995) and the amygdala has been reported to be specifically involved in the detection and early processing of stimuli not available to conscious awareness (Morris et al., 1999; Whalen et al., 1998). Therefore, the finding of increased anterior cingulate and amygdalar response in the non-marijuana smoking control subjects but not the chronic, heavy marijuana smokers during a masked affective paradigm is perhaps not unexpected. The relationship between both amount of use and overall cannabinoid concentration level and the BOLD signal changes suggest an effect of marijuana use in these regions which may impact the ability
