Marijuana use is also associated with atypical neural profiles. Adolescent marijuana users show a less efficient pattern of activation compared to non-users on working memory (Schweinsburg et al. 2008, 2010b), verbal learning (Schweinsburg et al. 2010a), and cognitive control (Tapert et al. 2007) tasks using fMRI. Brain response patterns in marijuana-using teens consistently indicate increased utilization of alternate brain networks (Jacobsen et al. 2007; Schweinsburg et al. 2005b; Tapert et al. 2007). In addition, users have demonstrated larger cerebellar volumes than non-users (Medina et al. 2010), and female marijuana users showed larger prefrontal cortex volumes than same-gender non-users (Medina et al. 2009), suggesting the possibility of attenuated synaptic pruning. White matter integrity is typically poorer in users than non-users, particularly in fronto-parietal circuitry and pathways connecting the frontal and temporal lobes (Bava et al. 2009). The functional implications of these differences appear disadvantageous, as marijuana-using teens show an increased susceptibility to depressive symptoms (Medina et al. 2007b) and poorer performance than non-users on neuropsychological tests of psychomotor speed, complex attention, verbal memory, planning, and sequencing ability, even after a month of sustained abstinence (Medina et al. 2007a).
