“Maintaining Memories with Marijuana. Research in my laboratory has demonstrated that stimulating the brain’s marijuana receptors may offer protection by reducing brain inflammation and by restoring neurogenesis. Thus, later in life, marijuana might actually help your brain, rather than harm it.

It takes very little marijuana to produce benefits in the older brain; my colleague in France, Dr. Yannick Marchalant, coined the motto “a puff is enough” because it appears as though only a single puff each day is necessary to produce significant benefit.

The challenge for pharmacologists in the future will be to isolate the beneficial effects of the marijuana plant from its psychoactive effects.”

http://www.theweedblog.com/does-smoking-marijuana-prevent-alzheimers-disease/