http://www.abc.net.au/science/articles/200...mp;topic=latest

‘Australian researchers have found that long-term heavy use of marijuana may cause parts of the brain to shrink.

Published in this month’s Archives of General Psychiatry, the study found that the hippocampus and amygdala were smaller in men who were heavy marijuana users compared to non-users.

The study looked at 15 men heavy marijuana users, who had smoked at least five marijuana cigarettes daily for on average of 20 years.

Brain scans showed that on average their hippocampus volume was 12% less and amygdala volume was 7% less than in the 16 men who were not marijuana users.

The hippocampus regulates memory and emotion, while the amygdala plays a critical role in fear and aggression.’