Is cannabis making you focus too much on irrelevant stimuli?

Is cannabis making you focus too much on irrelevant stimuli?

New study develops evidence on effect of cannabis on salience processing and how psychotic symptoms develop through the inappropriate attribution of salience to nonsalient stimuli.

Induction of Psychosis by {Delta}9-Tetrahydrocannabinol Reflects Modulation of Prefrontal and Striatal Function During Attentional Salience Processing 

Sagnik Bhattacharyya, MBBS, MD, PhD; José Alexandre Crippa, MD, PhD; Paul Allen, PhD; Rocio Martin-Santos, MD, PhD; Stefan Borgwardt, PhD; Paolo Fusar-Poli, MD; Katya Rubia, PhD; Joseph Kambeitz, MB; Colin O’Carroll, PhD; Marc L. Seal, PhD; Vincent Giampietro, PhD; Michael Brammer, PhD; Antonio Waldo Zuardi, MD, PhD; Zerrin Atakan, MD, FRCPsych; Philip K. McGuire, MD, PhD

Arch Gen Psychiatry. 2012;69(1):27-36. doi:10.1001/archgenpsychiatry.2011.161

Context: The aberrant processing of salience is thought to be a fundamental factor underlying psychosis. Cannabis can induce acute psychotic symptoms, and its chronic use may increase the risk of schizophrenia. We investigated whether its psychotic effects are mediated through an influence on attentional salience processing.

Objective: To examine the effects of {Delta}9-tetrahydrocannabinol ({Delta}9-THC) and cannabidiol (CBD) on regional brain function during salience processing.

Design: Volunteers were studied using event-related functional magnetic resonance imaging on 3 occasions after administration of {Delta}9-THC, CBD, or placebo while performing a visual oddball detection paradigm that involved allocation of attention to infrequent (oddball) stimuli within a string of frequent (standard) stimuli.

Setting: University center.

Participants: Fifteen healthy men with minimal previous cannabis use.

Main Outcome Measures: Symptom ratings, task performance, and regional brain activation.

Results: During the processing of oddball stimuli, relative to placebo, {Delta}9-THC attenuated activation in the right caudate but augmented it in the right prefrontal cortex. {Delta}9-Tetrahydrocannabinol also reduced the response latency to standard relative to oddball stimuli. The effect of {Delta}9-THC in the right caudate was negatively correlated with the severity of the psychotic symptoms it induced and its effect on response latency. The effects of CBD on task-related activation were in the opposite direction of those of {Delta}9-THC; relative to placebo, CBD augmented left caudate and hippocampal activation but attenuated right prefrontal activation. 

Conclusions: {Delta}9-Tetrahydrocannabinol and CBD differentially modulate prefrontal, striatal, and hippocampal function during attentional salience processing. These effects may contribute to the effects of cannabis on psychotic symptoms and on the risk of psychotic disorders.

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