The anterior cingulate, an area with a high concentration of CB-1 receptors, has been shown to play a key role in affective regulation and the inhibition of impulsive behavior (Devinsky et al., 1995). Results from investigations using PET and fMRI techniques have reported metabolic alterations within frontal regions of marijuana smokers, both at rest and during tasks which require executive function, inhibition, and decision making (Eldreth et al., 2004; Gruber and Yurgelun-Todd, 2005). Previous studies have demonstrated significant increases in cingulate activation that were associated with the level of both injected (Mathew et al., 1998; 2002) and smoked (O'Leary et al., 2000; 2002) marijuana. Studies have also reported high CB-1 receptor density within the human limbic system, including the amygdala, a critical brain region involved with affective processing (Joseph, 1996; Killgore and Yurgelun-Todd, 2004). Results from animal studies have suggested an interaction between cannabinoids and stress in the activation of the amygdala, which may provide a context for understanding the affective changes observed following marijuana use (Patel et al., 2005). Specifically, increased c-Fos expression has been shown within the central
