As hypothesized, chronic, heavy marijuana smokers demonstrated significant differences in both the magnitude and pattern of BOLD response within the cingulate and amygdala during the presentation of masked angry and masked happy faces relative to non-marijuana smoking control subjects. This was true, despite the fact that no significant between-group differences were noted for any clinical or demographic variable, with the exception of alcohol use, and all subjects appeared to be stable with regard to their mood. Specifically, ROI analyses revealed that the chronic, heavy marijuana smokers demonstrated relatively lower anterior cingulate and amygdalar activity during the presentation of masked angry stimuli sets relative to the non-marijuana smoking control subjects, who showed relatively higher activation within these regions during the task. In contrast, the chronic, heavy marijuana smokers demonstrated a larger, more diffuse pattern of activation during the presentation of masked happy faces within the cingulate as compared to the non-marijuana smoking control subjects, with no discernible increase in amygdalar activation. These differential patterns and magnitude of activation for the chronic, heavy marijuana smokers relative to the non-marijuana smoking control subjects underscore the likelihood that these subjects process emotional stimuli differently from those who do not smoke.
