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Marijuana-Schizophrenia Link in Brain Scans

December 8, 2005 - Marijuana use may raise the risk of schizophrenia among adolescents already predisposed to the disease, a New York based researcher has suggested.

The finding is based on a series of small brain-imaging studies by Manzar Ashtari, PhD, of Zucker Hillside Hospital in Glen Oaks, NY. Dr Ashtari has identified a region of the brain that she says is still "under construction" during adolescence, and is affected by both schizophrenia and marijuana use.

Dr Ashtari presented the results of her studies at a Radiological Society of North America (RSNA) podium presentation on 1 December, and her findings were summarized on 1 December 2005 in a report by MedPage Today.

The results of studies in adolescents and schizophrenics strongly support the hypothesis that using marijuana is a risk factor for developing schizophrenia "if the teenager has a family history of schizophrenia," Dr Ashtari reportedly said at a press conference sponsored by the RSNA.

Brain-Imaging Study

Dr Ashtari and colleagues followed microscopic changes in the brain's arcuate fasciculus using diffusion-tensor imaging, a sophisticated brain-imaging method. The resulting tensor images "provide a more in depth study of the brain than magnetic resonance, which images only static water molecules," said Dr Ashtari, according to MedPage Today.

Four studies compared images from 12 healthy young adolescent boys' brains with images from 12 healthy older teenage boys' brains. Results showed several areas of the arcuate fasciculus "are still developing during early adolescence."

The arcuate fasciculus is a fibrous bundle that connects Broca's area (in the frontal lobe) and Wernicke's area (in the left temporal lobe). It is involved in speech development, language interpretation and several other higher-order functions, according to Dr Ashtari.

The researchers also compared brain-scans from 11 people with schizophrenia with those of 17 healthy, matched controls; they also compared brain-scans from 17 people with schizophrenia who used marijuana with 17 healthy, matched controls. The fourth study compared brain-scans from 15 people who used marijuana with scans from 15 matched non-marijuana users.

"We found that marijuana affects areas of the brain that are still developing during adolescence and these are the same areas that are affected by schizophrenia," Dr Ashtari said, according to MedPage Today.

Interpreting the Data

Dr Ashtari's findings should be cautiously interpreted, says Michael Brant-Zawadzki, MD, chairman of the RSNA's communication committee. "The numbers are small and the studies are from a single institution," he reportedly said.

An additional confounding factor concerns the mechanism of how marijuana may be affecting brain function. According to Dr Brant-Zawadzki, the arcuate fasciculus is an area of the brain in which "myelination continues throughout adolescence. So it is difficult to say if marijuana is disrupting this myelination process or it is merely delaying the process or if this is a chance finding."

Dr Ashtari agreed that the results of these studies must be confirmed in larger trials.

RSNA: Brain Scans Suggest Marijuana-Schizophrenia Link, MedPage Today, 1 December 2005.
The Impact of Recurrent Exposure to Cannabis on Brain Development in Adolescents with Schizophrenia and Healthy Volunteers. Ashtari M et al, Radiological Society of North America.

Posted: December 2005