Regular marijuana use during adolescence, but not adulthood, may permanently impair cognition and increase the risk for psychiatric diseases, such as schizophrenia. Cortical oscillations (patterns of the activity of neurons in the brain and are believed to underlie the brain's various functions) are integral for cognitive processes and are abnormal in patients with schizophrenia. Dr. Asaf Keller, PhD, Professor of Anatomy and Neurobiology at the University of Maryland School of Medicine and senior author of study remarked "Previous research has shown that children who started using marijuana before the age of 16 are at greater risk of permanent cognitive deficits, and have a significantly higher incidence of psychiatric disorders such as schizophrenia. There likely is a genetic susceptibility, and then you add marijuana during adolescence and it becomes the trigger." For the study Dr. Asaf Keller, along with Sylvina Mullins Raver, a Ph.D. candidate in the Program in Neuroscience in the Department of Anatomy and Neurobiology at the University of Maryland School of Medicine and Sarah Paige Haughwout, a research technician in Dr. Keller's laboratory and co-author of study tested the hypothesis that adolescence is a sensitive period because of the active development of cortical oscillations and neuromodulatory systems that underlie them. The endocannabinoid system upon which marijuana acts is one such system. Raver commented "We wanted to identify the biological underpinnings and determine whether there is a real, permanent health risk to marijuana use." For the study researchers first examined cortical oscillations in mice and then exposed the young mice to very low doses of the active ingredient in marijuana (THC) for a span of 20 days and then returned the mice to their siblings and develop normally. Then the research team repeated the experiment by administering marijuana ingredients to adult mice that had never been exposed to the drug before. The adult mice cortical oscillations and their ability to perform cognitive behavioral tasks remained normal. This had indicated that it was only drug exposure during the critical period of adolescence that impaired cognition through this mechanism. Next, the research team attempted to identify the mechanisms underlying these changes and the time period in which they occur. According to Dr. Keller "we looked at the different regions of the brain." "The back of the brain develops first, and the frontal parts of the brain develop during adolescence. We found that the frontal cortex is much more affected by the drugs during adolescence. This is the area of the brain controls executive functions such as planning and impulse control. It is also the area most affected in schizophrenia." The team writes "These data establish a link between chronic adolescent cannabinoid exposure and alterations in adult cortical network activity that underlies cognitive processes." "We are hoping we will learn more about schizophrenia and other psychiatric disorders, which are complicated conditions. These cognitive symptoms are not affected by medication, but they might be affected by controlling these cortical oscillations," said Dr. Keller. Dr. E. Albert Reece, MD, PhD, MBA, Vice President for Medical Affairs, University of Maryland; the John Z. and Akiko K. Bowers Distinguished Professor, and Dean of the School of Medicine, professor in the departments of Obstetrics and Gynecology, Medicine, and Biochemistry & Molecular Biology, member of the prestigious Institute of Medicine (IOM) of the National Academy of Sciences commented "This study is an example of how the basic science research taking place in our state-of-the-art laboratories can impact human health and inform health policy." "We are proud of this groundbreaking discovery and look forward to watching this research develop further." This study is published in Neuropsychopharmacology, a publication of the journal Nature. Source
