(Undated) — A new study shows that even casual marijuana use can lead to big changes in the brain. Researchers at Northwestern University found that young adults who used marijuana just once or twice a week showed abnormalities in two key areas of the brain. The regions most affected are responsible for processing emotions, decision making and motivation. We see the evidence of this in Washington D.C. and I’m not kidding! The findings are published in “The Journal of Neuroscience.