Researchers looking at the effects of cannabis on the brain have made some interesting discoveries. The effect is similar to some of the symptoms of schizophrenia, say Dr. Matthew Jones and colleagues at Bristol University, UK. They predicted that the detrimental impact of cannabis on memory and cognition might be caused by brain networks being “disorchestrated.”
Normally, specific parts of the brain are tuned into each another at certain frequencies, say the researchers. This rhythmic activity produces brain waves and allows information to be processed in order for us to react.
The team used the analogy of an orchestra to explain how this works. They say that brain activity can be compared to the performance of an orchestra in which string, brass, woodwind and percussion sections are joined together in rhythms dictated by the conductor. In a similar way, specific structures in the brain tune in to one another at certain frequencies. Their rhythmic activity creates brain waves, and the tuning of these brain waves normally allows information to be processed that guides our behavior. But cannabis causes disturbances in systems involved in concentration and memory, the team found.
The primary psychoactive ingredient of cannabis, known as THC, activates cannabinoid receptors, which are found in many brain areas. In the research, the team measured the electrical activity from hundreds of neurons in rats when given a drug similar to THC which also stimulates cannabinoid receptors.
This showed that the effects on individual brain regions were subtle, but brain waves across the hippocampus and prefrontal cortex were completely disrupted. These two brain areas are vital for memory and decision-making, so the rats were no longer able to accurately navigate a maze. Both areas are also involved in schizophrenia.
Findings are published in the Journal of Neuroscience. The authors write that these results show a possible mechanism behind the cognitive impairment caused by cannabis that was described by Dr Frederick T. Melges and his team back in 1970. Dr. Melges called the effect “temporal disintegration,” and described it as “difficulty in retaining, coordinating and serially indexing those memories, perceptions and expectations that are relevant to the goal one is pursuing.”
More recent studies suggest that THC given intravenously to healthy volunteers can induce several psychotic symptoms of schizophrenia, so the authors believe that THC studies be used to model broader aspects of the disease, not just cognitive dysfunction.
Dr. Jones commented, “Marijuana abuse is common among sufferers of schizophrenia and recent studies have shown that the psychoactive ingredient of marijuana can induce some symptoms of schizophrenia in healthy volunteers. These findings are therefore important for our understanding of psychiatric diseases, which may arise as a consequence of ‘disorchestrated brains’ and could be treated by re-tuning brain activity.”
Co-author Michal Kucewicz added, “These results are an important step forward in our understanding of how rhythmic activity in the brain underlies thought processes in health and disease.”
The researchers conclude, “These tools will continue to shed light on the neural mechanisms of working memory and decision making in health and disease.”
A 2012 review of current knowledge shows that the endocannabinoid system in the brain has a major role in schizophrenia. “Data reported so far clearly indicate the presence of a dysregulation in the endocannabinoid system in animal models of psychosis as well as in schizophrenic patients,” the review says.
Its authors, led by Professor Daniela Parolaro of the University of Insubria, Italy, add that animal models suggest that adolescence is “a highly vulnerable age for the consequences of cannabis exposure on different domains (such as cognition and social behavior) that are altered in psychotic disorders.”
They suggest that drugs which target the cannabinoid system are “a new therapeutic possibility for psychotic disorders.” However, they warn that drug studies so far have not had straightforward results, with different types of drug showing different effects.
But despite all these limitations, cannabidiol, a compound found in cannabis that activates cannabinoid receptors, has shown fairly consistent antipsychotic properties in animal tests. Recent studies indicate that cannabidiol may be as effective as antipsychotics in treating schizophrenia.
The benefit of cannabidiol appears similar to that gained from atypical antipsychotic drugs, and so far it is considered a safe and well-tolerated compound. Future studies will need to compare its antipsychotic effects against standard drugs for schizophrenic patients.
Kucewicz, M. T. et al. Dysfunctional Prefrontal Cortical Network Activity and Interactions following Cannabinoid Receptor Activation. Journal of Neuroscience, published online October 25, 2011.
Zamberletti, E., Rubino, T. and Parolaro, D. The endocannabinoid system and schizophrenia: integration of evidence. Current Pharmaceutical Design, published online June 7, 2012.