You can't die from smoking too much pot, a THC overdose is borderline impossible, the sheer mechanics behind it are mind-boggling according to most sources, these deaths due to weed you're thinking of are most likely the result of these people smoking laced weed (as in laced with stuff like PCP, cocaine, and in some circumstances, chemical agents) I know a girl who smoked weed laced with windex, it wasnt a pretty sight afterwards..anyways, off topic.

Dead brain cells are most likely the result of holding in the smoke far too long and the lack of oxygen kills them.

It's good you came to the boards rather then take the information whole without questioning it, todays society expects people to question their surroundings, props to ya