A Study on the Brain’s Addiction to Drugs

What happens in your brain when you ingest a drug? Some drugs, such as marijuana and heroin, have a similar structure to chemical messengers, called neurotransmitters, which are naturally produced by the brain. Because of this similarity, these drugs are able to “fool” the brain's receptors and activate nerve cells to send abnormal messages.

A study conducted by Dr. Jodi Gilman at Massachusetts General Hospital-Harvard Center for Addiction Medicine involved scanning the brains of 20 pot smokers, ages 18 to 25. What she and fellow researchers at Harvard and Northwestern University found within those scans surprised them. Even in the seven participants who smoked only once or twice a week, there was evidence of structural differences in two significant regions of the brain. The more the subjects smoked, the greater the differences.

However, some marijuana use by healthy adults seems to pose minimal risk and may even be slightly beneficial in some cases. However, , with the brain developing into the mid-20s, young people who smoke early and often are more likely to have learning and mental health problems. In the Harvard-Northwestern study, differences between the brains of young adult marijuana smokers and those of nonsmokers are shown in the diagram. In these composite scans, colors represent the differences — in the shape of the amygdala, top, and nucleus accumbens. Yellow indicates areas that are most different, red the least.

This study, however, was preliminary and small; the team scanned the brains of only 40 young adults, most from Boston-area colleges. Half were nonusers; half reported smoking for one to six years and showed no signs of dependence. Besides the seven light smokers, nine used three to five days a week and four used, on average, daily. All smokers showed abnormalities in the shape, density and volume of the nucleus accumbens, which “is at the core of motivation, the core of pleasure and pain, and every decision that you make,” explained Dr. Hans Breiter, a co-author of the study and professor of psychiatry and behavioral sciences at Northwestern’s medical school. Attempts to replicate the study on a larger scale are underway.