Marijuana Ingredients - How Does Brain Functioning React To Visual Stimuli?

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Main Category: Alcohol / Addiction / Illegal Drugs
Also Included In: Psychology / Psychiatry;  Neurology / Neuroscience
Article Date: 05 Jan 2012 - 8:00 PST


A report in the January issue of Archives of General Psychiatry, one of the JAMA/Archives journals shows that different ingredients in marijuana seem to affect brain regions differently during brain processing functions that involve responses to certain visual stimuli and tasks.

Dr. Sagnik Bhattacharyya, at the Institute of Psychiatry at King's College in London and his team examined 15 healthy men, who were occasional marijuana users, to assess the effects of delta9-tetrahydrocannabinol (delta9-THC) and cannabidiol (CBD) on regional brain function during salience processing, a process of how people perceive their surroundings.

The researchers administered all participants with either delta9-THC, CBD or placebo, after which they performed functional MRI imaging on three occasions to study each participant. To measure attentional salience processing, the researchers gave the participants a visual oddball task to perform, in which they had to press buttons according to the direction of arrows pointing on a screen.

The researchers declare:

"Pair wise comparisons revealed that delta9-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 observed that on reaction time to nonsalient relative to salient stimuli, the effect of delta9-THC was greater compared with placebo. This was linked to modulation of both prefrontal and striatal function by delta9-THC, increasing the activation in the former region and weakening it in the latter.

The researchers explain:

"Moreover, in the present study, the magnitude of delta9-THC's effect on response times to nonsalient stimuli was correlated with its effect on activation in the right caudate, the region where the physiological effect of delta9-THC was linked to its induction of psychotic symptoms. Collectively, these observations suggest that delta9-THC may increase the aberrant attribution of salience and induce psychotic symptoms through its effects on the striatum and lateral prefrontal cortex."

When the researchers compared the effects of CBD with delta9-THC and placebo in terms of the visual task, they discovered a "significant effect" in the left caudate with CBD increasing the response and delta9-THC weakening it.

They conclude:

"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."

Written by Petra Rattue
Copyright: Medical News Today
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