they had munkeys smoke a bitch load of bud in an enclosed area and compared their brain cell count to a munkey who has never smoked. the one that smoked the weed had a smaller amount. however what people don't seem to see is that the munkey didn't loose the brain cells due to weed, but because of oxygen depravtion. there wasn't enough oxygen getting to its brain which caused it to loose brain cells. WEED DOESN'T MAKE YOU LOOSE BRAIN CELLS, people who preech it do.