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Effects of Marijuana on Brain Function

by Sheela Philomena on  January 3, 2012 at 2:52 PM Alcohol & Drug Abuse News   - G J E 4
Ingredients present in marijuana affect brain processing functions involving responses to certain visual stimuli and tasks.
 Effects of Marijuana on Brain Function
Effects of Marijuana on Brain Function
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Sagnik Bhattacharyya, M.B.B.S., M.D., Ph.D, at the Institute of Psychiatry, King's College in London, and colleagues studied 15 healthy men, who were occasional marijuana users, to examine the effects of 9-tetrahydrocannabinol (9-THC) and cannabidiol (CBD) on regional brain function during salience processing, which is how people perceive things around them.

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The authors used functional MRI images to study each participant on three occasions after administration of 9-THC, CBD or placebo. Study participants performed a visual oddball task of pressing buttons according to the direction arrows on a screen were pointing, as a measure of attentional salience processing.

"Pairwise comparisons revealed that 9-THC significantly increased the severity of psychotic symptoms compared with placebo and CBD whereas there was no significant difference between the CBD and placebo conditions," the researchers said.

9-THC had a greater effect than placebo on reaction time to non-salient relative to salient stimuli.

This was associated with modulation of both prefrontal and striatal function by 9-THC, augmenting (increasing) activation in the former region and attenuating (weakening) it in the latter.

"Moreover, in the present study, the magnitude of 9-THC's effect on response times to non-salient stimuli was correlated with its effect on activation in the right caudate, the region where the physiological effect of 9-THC was linked to its induction of psychotic symptoms," they wrote.

They concluded that "collectively, these observations suggest that 9-THC may increase the aberrant attribution of salience and induce psychotic symptoms through its effects on the striatum and lateral prefrontal cortex."

When the effects of CBD were contrasted with 9-THC and placebo with respect to the visual task there was a "significant effect" in the left caudate with CBD augmenting (increasing) the response and 9-THC attenuating (weakening) it.

"These effects suggest that CBD may also influence the effect of cannabis use on salience processing - and hence psychotic symptoms - by having an opposite effect, enhancing the appropriate response to salient stimuli," the researchers added.

The findings appeared in the January issue of Archives of General Psychiatry, one of the JAMA/Archives journals.

Source: ANI
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