Heavy Marijuana Use Damages Adolescent Brains

CHICAGO (Reuters) - Adolescents who regularly smoke marijuana risk damaging a key brain pathway associated with language development and some predisposed to schizophrenia may develop the illness early, researchers said on Wednesday.

Brain scans revealed microscopic abnormalities in a region of the brain that governs higher aspects of language and listening functions in adolescents who are heavy marijuana smokers.

Similar damage to the bundle of fibers, called the arcuate fasciculus, that connect the Broca's area in the left frontal lobe and the Wernicke's area in the left temporal lobe was found in the brains of marijuana smokers and schizophrenics studied.

"These findings suggest that in addition to interfering with normal brain development, heavy marijuana use in adolescents may also lead to an earlier onset of schizophrenia in individuals who are genetically predisposed to the disorder," said psychiatry professor Sanjiv Kumra of the Albert Einstein College of Medicine in New York.

The researchers scanned the brains of 114 subjects, 26 of whom were selected because they were diagnosed schizophrenics. Of the schizophrenic group, 15 smoked marijuana.

Another 15 subjects were nonschizophrenic adolescent male marijuana smokers who were matched against nonsmokers. It was those smokers whose scans showed abnormalities in the language and listening pathway.

The brain's language pathway continues to develop during adolescence and is susceptible to neurotoxins introduced through marijuana use, the researchers said.

A scanning technique called diffusion tensor imaging that detects and measures the motion of water molecules in the brain was used in the study, which was presented at the annual meeting of the Radiological Society of North America. The technique is not used to diagnose schizophrenia.

Roughly 3 million Americans 12 years of age or older use marijuana on a daily or almost daily basis, according to the National Institute on Drug Abuse. The researchers said longer-term studies are needed to determine if the brain abnormalities observed in adolescents are permanent.