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David Baxter

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Neurophysiological link between cannabis use and schizophrenia found

Researchers have found altered neural synchronization in people who smoke cannabis, providing evidence to support the link between the use of this drug and schizophrenia.

Altered neural synchronization has previously been demonstrated in patients with schizophrenia. This led Patrick Skosnik (Indiana University, Bloomington, USA) and team to suggest that such alterations may represent a neurophysiological link between schizophrenia symptoms and the neurobehavioral effects of cannabis.

The researchers assessed neural synchronization using electroencephalograms (EEG) to measure auditory steady-state potentials, eg, auditory click trains at specific frequencies - 20, 30, and 40 Hz - in 17 cannabis users and 16 drug na?ve individuals.

The cannabis users showed decreased EEG power and signal-to-noise ratio at the stimulation frequency of 20 Hz compared with non-drug users.

Skosnik and colleagues note that there was no significant difference between the two groups with regard to noise power, indicating that the altered neural synchronization in cannabis users was due to decreased signal strength of oscillating circuits and not the increased noise stemming from neural background activity.

The cannabis users also demonstrated increased schizotypal personality characteristics, as assessed on the Schizotypal Personality Questionnaire, compared with controls. However, there was no significant difference between the two groups in scores on the Wechsler Adult Intelligence Scale. This demonstrates that any alterations in neural synchrony were not associated with generalized cognitive or sensory deficits, the researchers note.

Further analysis revealed that scores on the Schizotypal Personality Questionnaire positively correlated with total years of cannabis use. In addition, schizotypy scores negatively correlated with 20 Hz power, indicating that cannabis-using individuals scoring higher in schizotypy had larger deficits in neural synchronization.

"These data provide evidence for neural synchronization and early-stage sensory processing deficits in cannabis use," the team writes in the American Journal of Psychiatry.

"Given that there is tight coupling of the endocannabinoid and dopamine systems, it appears possible that genetic anomalies leading to altered dopamine activity may interact with early cannabis exposure to produce overt psychosis."

Am J Psychiatry 2006; 163: 1798-1805
 

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