Researchers have found structural changes in the brains of marijuana smokers ages 18 to 25. The severity of the changes is linked with the amount of drug use, but even casual pot smokers experienced some effect. The changes, scientists believe, lead to enhanced
sensations of pleasure and reward from the effect of the drug.
Each hemisphere of the brain has a structure called the nucleus accumbens. The nucleus accumbens is involved in perceiving pleasure and reward as well as fear and addiction. Each hemisphere also contains an almond-shaped structure called the amygdala. The amygdala plays a role in forming memories of emotional events.
Researchers found that the density of brain matter in the nucleus accumbens and amygdala was increased in heavy pot smokers, and the size of the structures was increased. The differences were directly related to the amount of marijuana smoked.