A systematic review of 17 studies (13 meeting inclusion criteria) examined cannabis's effects on impulsivity, disinhibition, and motor control, with a focus on neuroimaging findings from acute and chronic use up to May 2012. Functional imaging studies indicate that chronic cannabis users have lower prefrontal blood flow than controls, while acute administration of THC or marijuana increases brain metabolism in several regions during impulsivity tasks. Structural imaging studies found reduced prefrontal volumes and white matter integrity in cannabis users, which may mediate abnormal impulsivity and mood. The review concludes that more longitudinal studies are needed to determine whether impulsivity precedes cannabis use or cannabis aggravates impulsivity and discontinuation.
A systematic review compared resting-state cerebral blood flow patterns in first-episode psychosis (FEP), acute cannabinoid intoxication, and acute opioid intoxication. The evidence was highly conflicting within each condition, but some consistent findings emerged: both positive symptoms of FEP and depersonalization after cannabis administration were linked to increased activity in the anterior cingulate cortex, a key region of the default mode network. The review included 22 studies with 279 FEP participants or controls, 315 participants receiving cannabinoids, and 113 receiving opioids.