The principal active component of marijuana, delta9-tetrahydrocannabinol (delta9-THC), produces complex alterations in cognition and behavior (Fant, Heishman, Bunker, & Pickworth, 1998; Johns, 2001; Solowij et al., 2002). Brain regions with high densities of cannabinoid receptors include the frontal cortex, hippocampus, basal ganglia, cerebellum, amygdala, and striatum (Eggan & Lewis, 2006; Freedland, Whitlow, Miller, & Porrino, 2002; Pontieri, Conti, Zocchi, Fieschi, & Orzi, 1999; Quickfall & Crockford, 2006). Human studies provide evidence for increased metabolism (Block et al., 2002; Mathew et al., 2002), decreased gray matter density (Matochik, Eldreth, Cadet, & Bolla, 2005) and atypical activation within these regions (Eldreth, Matochik, Cadet, & Bolla, 2004; Kanayama, Rogowska, Pope, Gruber, & Yurgelun-Todd, 2004). Similarly, chronic alcohol exposure is associated with cortical and white matter (WM) volume loss in the hippocampus, cingulate, corpus callosum, cerebellum, and frontal brain regions (De Bellis et al., 2000; De Bellis et al., 2005; Harris et al., 2008; Medina et al., 2008; Nagel, Schweinsburg, Phan, & Tapert, 2005; Pfefferbaum, Adalsteinsson, & Sullivan, 2006a).
