"It is the story of nature vs. nurture," said Manzar Ashtari, an associate professor in radiology and psychiatry at Albert Einstein College of Medicine in the Bronx and a scientist at LIJ's Zucker Hillside Hospital in Glen Oaks. "If there are people who are vulnerable and smoke marijuana, they may be putting themselves at greater risk for developing severe mental illness."

Ashtari and her co-investigator, child psychiatrist Dr. Sanjiv Kumra, found that a brain region called the arcuate nucleus, a bundle of fibers that connects the front of the brain to deeper regions, is underdeveloped in both schizophrenia patients and in marijuana users. While the lack of growth seems to be only on the left side in these teenagers, schizophrenia patients who also abuse marijuana showed problems on both sides of the brain.