A study by researchers at the University of Iowa shows frequent use of marijuana does cause some major changes in your brain. Researcher Robert Block says they compared frequent marijuana smokers with those who don’t use the drug.Marijuana users showed lower blood flow to the rear of their brain. He says the decreased blood flow brought on by the pot could have several implications.There’s evidence that part of the brain is involved in memory and attention. Brock says the study only shows what happens in the short-term when people smoke marijuana.Brock says more study’s necessary to determine the long-term impact of smoking marijuana.Brock will join other researchers next week at a conference at the University to discuss the medical use of marijuana.